Wireless communication method and wireless communication terminal

ABSTRACT

Provided is a wireless communication terminal. The wireless communication terminal includes a transceiver configured to transmit/receive a wireless signal, and a processor configured to control an operation of the wireless communication terminal. The transceiver receives a trigger frame including information on a channel to be used, by a plurality of wireless communication terminals including the wireless communication terminal, in communication with a base wireless communication terminal that is any one wireless communication terminal different from the plurality of wireless communication terminals.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/502,202, filed Feb. 6, 2017, which is a U.S. National StageApplication under 35 U.S.C. § 371 of PCT Application No.PCT/KR2015/008314, filed Aug. 7, 2015, which claims priority to KoreanPatent Application No's. 10-2014-0101776, filed Aug. 7, 2014,10-2014-0109433, filed Aug. 22, 2014, 10-2014-0114610, filed Aug. 29,2014, 10-2014-0143125 filed Oct. 22, 2014, 10-2015-0035127 filed Mar.13, 2015 and 10-2015-0066669 filed May 13, 2015, whose entiredisclosures are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a wireless communication method and awireless communication terminal for setting a broadband link. Morespecifically, the present invention relates to a wireless communicationmethod and a wireless communication terminal for increasing datacommunication efficiency by expanding a data transmission bandwidth of aterminal.

BACKGROUND ART

In recent years, with supply expansion of mobile apparatuses, a wirelessLAN technology that can provide a rapid wireless Internet service to themobile apparatuses has been significantly spotlighted. The wireless LANtechnology allows mobile apparatuses including a smart phone, a smartpad, a laptop computer, a portable multimedia player, an embeddedapparatus, and the like to wirelessly access the Internet in home or acompany or a specific service providing area based on a wirelesscommunication technology in a short range.

Institute of Electrical and Electronics Engineers (IEEE) 802.11 hascommercialized or developed various technological standards since aninitial wireless LAN technology is supported using frequencies of 2.4GHz. First, the IEEE 802.11b supports a communication speed of a maximumof 11 Mbps while using frequencies of a 2.4 GHz band. IEEE 802.11a whichis commercialized after the IEEE 802.11b uses frequencies of not the 2.4GHz band but a 5 GHz band to reduce an influence by interference ascompared with the frequencies of the 2.4 GHz band which aresignificantly congested and improves the communication speed up to amaximum of 54 Mbps by using an OFDM technology. However, the IEEE802.11a has a disadvantage in that a communication distance is shorterthan the IEEE 802.11b. In addition, IEEE 802.11g uses the frequencies ofthe 2.4 GHz band similarly to the IEEE 802.11b to implement thecommunication speed of a maximum of 54 Mbps and satisfies backwardcompatibility to significantly come into the spotlight and further, issuperior to the IEEE 802.11a in terms of the communication distance.

Moreover, as a technology standard established to overcome a limitationof the communication speed which is pointed out as a weak point in awireless LAN, IEEE 802.11n has been provided. The IEEE 802.11n aims atincreasing the speed and reliability of a network and extending anoperating distance of a wireless network. In more detail, the IEEE802.11n supports a high throughput (HT) in which a data processing speedis a maximum of 540 Mbps or more and further, is based on a multipleinputs and multiple outputs (MIMO) technology in which multiple antennasare used at both sides of a transmitting unit and a receiving unit inorder to minimize a transmission error and optimize a data speed.Further, the standard can use a coding scheme that transmits multiplecopies which overlap with each other in order to increase datareliability.

As the supply of the wireless LAN is activated and further, applicationsusing the wireless LAN are diversified, the need for new wireless LANsystems for supporting a higher throughput (very high throughput (VHT))than the data processing speed supported by the IEEE 802.11n has comeinto the spotlight. Among them, IEEE 802.11ac supports a wide bandwidth(80 to 160 MHz) in the 5 GHz frequencies. The IEEE 802.11ac standard isdefined only in the 5 GHz band, but initial 11ac chipsets will supporteven operations in the 2.4 GHz band for the backward compatibility withthe existing 2.4 GHz band products. Theoretically, according to thestandard, wireless LAN speeds of multiple stations are enabled up to aminimum of 1 Gbps and a maximum single link speed is enabled up to aminimum of 500 Mbps. This is achieved by extending concepts of a radiointerface accepted by 802.11n, such as a wider radio frequency bandwidth(a maximum of 160 MHz), more MIMO spatial streams (a maximum of 8),multi-user MIMO, and high-density modulation (a maximum of 256 QAM).Further, as a scheme that transmits data by using a 60 GHz band insteadof the existing 2.4 GHz/5 GHz, IEEE 802.11ad has been provided. The IEEE802.11ad is a transmission standard that provides a speed of a maximumof 7 Gbps by using a beamforming technology and is suitable for high hitrate moving picture streaming such as massive data or non-compression HDvideo. However, since it is difficult for the 60 GHz frequency band topass through an obstacle, it is disadvantageous in that the 60 GHzfrequency band can be used only among devices in a short-distance space.

Meanwhile, in recent years, as next-generation wireless LAN standardsafter the 802.11ac and 802.11ad, discussion for providing ahigh-efficiency and high-performance wireless LAN communicationtechnology in a high-density environment is continuously performed. Thatis, in a next-generation wireless LAN environment, communication havinghigh frequency efficiency needs to be provided indoors/outdoors underthe presence of high-density stations and access points (APs) andvarious technologies for implementing the communication are required.

Especially, as the number of devices using a wireless LAN increases, itis necessary to efficiently use a predetermined channel. Therefore,required is a technology capable of efficiently using bandwidths bysimultaneously transmitting data between a plurality of stations andAPs.

DISCLOSURE Technical Problem

Accordingly, the present invention is directed to a wirelesscommunication method and a wireless communication terminal thatsubstantially obviate one or more of the problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide an efficient wirelesscommunication method and wireless communication terminal.

Another object of the present invention is to provide a wirelesscommunication method and a wireless communication terminal for allowingan access point to transmit data to a plurality of stations at the sametime and a plurality of stations to transmit data to an access point atthe same time.

Technical Solution

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, there isprovided a wireless communication terminal including: a transceiverconfigured to transmit/receive a wireless signal; and a processorconfigured to control an operation of the wireless communicationterminal, wherein the transceiver receives a trigger frame includinginformation on a channel to be used, by a plurality of wirelesscommunication terminals including the wireless communication terminal,in communication with a base wireless communication terminal that is anyone wireless communication terminal different from the plurality ofwireless communication terminals.

The processor may obtain the information on the channel to be used incommunication with the base wireless communication terminal based on thetrigger frame, and the transceiver may transmit data to the basewireless communication terminal based on the information on the channelto be used in communication with the wireless communication terminal.

The transceiver may transmit to the base wireless communication terminala frame indicating whether there is data to be transmitted from thewireless communication terminal to the base wireless communicationterminal.

A more data field included in the frame indicating whether there is datato be transmitted may indicate whether there is data to be transmittedfrom the wireless communication terminal to the base wirelesscommunication terminal.

The frame indicating whether there is data to be transmitted may be atleast one of a Acknowledgement (ACK) frame indicating that a frame isreceived successfully, a block ACK frame indicating that a plurality offrames are received successfully, and a frame including uplink datatransmitted from the wireless communication terminal to the basewireless communication terminal.

The frame indicating whether there is data to be transmitted may includeat least one of a size of data to be transmitted to the base wirelesscommunication terminal and information on an available channel detectedby the wireless communication terminal.

The processor may obtain the information on the channel to be used incommunication with the base wireless communication terminal based on thetrigger frame, and the transceiver may receive data from the basewireless communication terminal based on the information on the channelto be used in communication with the base wireless communicationterminal.

The transceiver may receive a Ready To Send (RTS)-to-Self frame from thebase wireless communication terminal and transmit a Clear To Send (CTS)frame notifying that reception is ready to the base wirelesscommunication terminal; and a reception address field of an RTS frame,that is, the RTS-to-Self frame, indicating that there is data to betransmitted may be a wireless communication terminal that transmits theRTS frame.

A data airtime of data received from the base wireless communicationterminal may be synchronized with a data airtime of data transmitted toanother wireless communication terminal different from the wirelesscommunication terminal.

The trigger frame may include information on a channel having abandwidth of more than a minimum unit frequency bandwidth used incommunication by the base wireless communication terminal andinformation on a sub-channel having a bandwidth of less than the minimumunit frequency bandwidth as a sub-band of the channel.

The information on the channel may be an index indicating the channeland the information on the sub-channel may be an index indicating thesub-channel.

According to another aspect of the present invention, there is provideda base wireless communication terminal including: a transceiverconfigured to transmit/receive a wireless signal; and a processorconfigured to control an operation of the base wireless communicationterminal, wherein the processor allocates a channel to be used incommunication with the base wireless communication terminal to aplurality of wireless communication terminals and transmits a triggerframe including information on the channel allocated to the plurality ofwireless communication terminals to the plurality of wirelesscommunication terminals.

The transceiver may receive data from a second wireless communicationterminal that is any one among the plurality of wireless communicationterminals through a channel allocated to the second wirelesscommunication terminal.

The transceiver may receive a frame indicating that there is data to betransmitted from the second wireless communication terminal to the basewireless communication terminal, from the second wireless communicationterminal, and transmit the trigger frame based on the received frame.

A more data field included in the frame indicating whether there is datato be transmitted may indicate whether there is data to be transmittedfrom the wireless communication terminal to the base wirelesscommunication terminal.

The frame indicating whether there is data to be transmitted may be atleast one of a Acknowledgement (ACK) frame indicating that a frame isreceived successfully, a block ACK frame indicating that a plurality offrames are received successfully, and a frame including uplink datatransmitted from the wireless communication terminal to the basewireless communication terminal.

The frame indicating whether there is data to be transmitted may includeat least one of a size of data to be received from the second wirelesscommunication terminal and information on an available channel detectedby the second wireless communication terminal.

The processor may allocate a channel to be used in communication withthe plurality of wireless communication terminals to the plurality ofwireless communication terminals based on the frame indicating whetherthere is data to be transmitted.

The information on the channel may be an index indicating the channeland the information on the sub-channel may be an index indicating thesub-channel.

According to a further another aspect of the present invention, there isprovided an operating method of a wireless communication terminal. Themethod includes: receiving, by a plurality of wireless communicationterminals including the wireless communication terminal, a trigger frameincluding information on a channel to be used in communication with abase wireless communication terminal that is any one wirelesscommunication terminal different from the plurality of wirelesscommunication terminals; and transmitting data to the base wirelesscommunication terminal or receiving data from the base wirelesscommunication terminal based on the information on the channel.

Advantageous Effects

One embodiment of the present invention provides an efficient wirelesscommunication method and wireless communication terminal.

Especially, one embodiment of the present invention is to provide awireless communication method and a wireless communication terminal forallowing an access point to transmit data to a plurality of stations atthe same time and a plurality of stations to transmit data to an accesspoint at the same time.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a wireless LAN system according to anembodiment of the present invention.

FIG. 2 is a view illustrating a wireless LAN system according to anotherembodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of a stationaccording to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of an accesspoint according to an embodiment of the present invention.

FIG. 5 is a view illustrating a process that a station sets an accesspoint and a link according to an embodiment of the present invention.

FIG. 6 is a view illustrating a structure of a poll frame according toan embodiment of the present invention.

FIG. 7 is a view illustrating a structure of a poll frame according toanother embodiment of the present invention.

FIG. 8 is a view illustrating a structure of a CH vector field in a pollframe according to an embodiment of the present invention.

FIG. 9 is a view illustrating a channel index in a frequency band of 5GHz according to an embodiment of the present invention.

FIG. 10 is a view illustrating a channel index in a frequency band of 5GHz according to another embodiment of the present invention.

FIG. 11 is a view illustrating a sub-channel index in a frequency bandof 20 MHz according to an embodiment of the present invention.

FIG. 12 is a view illustrating a sub-channel index in a frequency bandof 20 MHz according to another embodiment of the present invention.

FIG. 13 is a view illustrating a sub-channel index in a frequency bandof 20 MHz including a combination of non-contiguous sub-bands accordingto another embodiment of the present invention.

FIG. 14 is a view illustrating a preamble including sub-channelinformation according to an embodiment of the present invention.

FIG. 15 is a view illustrating a preamble including sub-channelinformation according to another embodiment of the present invention.

FIG. 16 is a view illustrating a preamble including sub-channelinformation according to another embodiment of the present invention.

FIG. 17 is a view illustrating a preamble including sub-channelinformation according to another embodiment of the present invention.

FIG. 18 is a view illustrating a CH vector field indicating acombination of non-contiguous sub-band channels according to anotherembodiment of the present invention.

FIG. 19 is a view illustrating a structure of an RTS-to-Self frameaccording to an embodiment of the present invention.

FIG. 20 is a view illustrating that an access point according to anembodiment of the present invention simultaneously transmits data to aplurality of stations using an RTS-to-Self frame.

FIG. 21 is a view illustrating that an access point according to anotherembodiment of the present invention simultaneously transmits data to aplurality of stations using an RTS-to-Self frame.

FIG. 22 is a view illustrating that an access point according to anembodiment of the present invention allocates one channel to each of aplurality of stations and asynchronously transmits data to the pluralityof stations.

FIG. 23 is a view illustrating that an access point according to anembodiment of the present invention allocates one or more channels toeach of a plurality of stations and asynchronously transmits data to theplurality of stations.

FIG. 24 is a view illustrating that an access point according to anembodiment of the present invention allocates one channel to each of aplurality of stations and synchronously transmits data to the pluralityof stations.

FIG. 25 is a view illustrating that an access point according to anembodiment of the present invention allocates one or more channels toeach of a plurality of stations and synchronously transmits data to theplurality of stations.

FIG. 26 is a view illustrating that an access point according to anembodiment of the present invention transmits data to a plurality ofstations when not receiving a CTS frame from any one station.

FIG. 27 is a view illustrating an operation of an access point tosimultaneously transmit data to a plurality of stations when the accesspoint is not able to simultaneously receive data from the plurality ofstations according to another embodiment of the present invention.

FIG. 28 is a view illustrating that when an access point according to anembodiment of the present invention transmits data to a plurality ofstations, after a PIFS elapses from the time when the access pointtransmits a poll frame to the plurality of stations, the plurality ofstations transmit a CTS frame to the access point.

FIG. 29 is a view illustrating that an access point according to anembodiment of the present invention transmits a poll frame to aplurality of stations and transmits data after transmitting anRTS-to-Self frame.

FIG. 30 is a view illustrating that an access point according to anembodiment of the present invention transmits data to a plurality ofstations using an M-RTS frame.

FIG. 31 is a view illustrating that a plurality of stations according toan embodiment of the present invention transmit data to an access pointafter receiving data from the access point.

FIG. 32 is a view illustrating that each of a plurality of stationsaccording to an embodiment of the present invention transmits data to anaccess point through a channel used when the access point transmits datato each of the plurality of stations.

FIG. 33 is a view illustrating that a plurality of stations according toan embodiment of the present invention receive an allocated channel totransmit data to an access point regardless of whether the access pointuses a corresponding channel when transmitting data to the plurality ofstations.

FIG. 34 is a view illustrating that an access point according to anembodiment of the present invention allocates a channel to a pluralityof stations based on information on an available channel transmitted bya station, and the plurality of stations transmit data to the accesspoint according to the allocated channel.

FIG. 35 is a view illustrating that an access point according to anembodiment of the present invention obtains a TXOP through a contentionprocedure and a CTS-to-Self frame, and a plurality of stations transmitdata to the access point.

FIG. 36 is a view illustrating data transmission between an access pointand a plurality of stations when there is no data to be transmitted tothe access point by some of the plurality of stations according to anembodiment of the present invention.

FIG. 37 is a view illustrating data transmission between an access pointand a plurality of stations when there is no data to be transmitted tothe access point by the plurality of stations according to an embodimentof the present invention.

FIG. 38 is a view illustrating that an access point according to anotherembodiment of the present invention transmits a trigger frame to aplurality of stations.

FIG. 39 is a view illustrating a structure of a frame indicating whetherthere is data to be transmitted to an access point by a stationaccording to another embodiment of the present invention.

FIG. 40 is a view illustrating that a plurality of stations according toanother embodiment of the present invention notifies an access pointwhether there is data to be transmitted through an ACK frame.

FIG. 41 is a view illustrating that a plurality of stations according toanother embodiment of the present invention notifies an access pointwhether there is data to be transmitted through an uplink transmissiondata frame.

FIG. 42 is a ladder diagram illustrating an operation in which a firstwireless communication terminal transmits data to a second wirelesscommunication terminal according to an embodiment of the presentinvention.

FIG. 43 is a ladder diagram illustrating an operation in which a secondwireless communication terminal transmits data to a first wirelesscommunication terminal according to an embodiment of the presentinvention.

MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstructed as limited to the embodiments set forth herein. Parts notrelating to description are omitted in the drawings in order to clearlydescribe the present invention and like reference numerals refer to likeelements throughout.

Furthermore, when it is described that one comprises (or includes orhas) some elements, it should be understood that it may comprise (orinclude or has) only those elements, or it may comprise (or include orhave) other elements as well as those elements if there is no specificlimitation.

This application claims priority to and the benefit of Korean PatentApplication Nos. 10-2014-0101776, Nos. 10-2014-0109433, Nos.10-2014-0114610, Nos. 10-2014-0143125, Nos. 10-2015-0035127, and Nos.10-2015-0066669 filed in the Korean Intellectual Property Office and theembodiments and mentioned items described in the respective applicationsare included in the Detailed Description of the present application.

FIG. 1 is a diagram illustrating a wireless LAN system according to anembodiment of the present invention. The wireless LAN system includesone or more basic service sets (BSS) and the BSS represents a set ofapparatuses which are successfully synchronized with each other tocommunicate with each other. In general, the BSS may be classified intoan infrastructure BSS and an independent BSS (IBSS) and FIG. 1illustrates the infrastructure BSS between them.

As illustrated in FIG. 1, the infrastructure BSS (BSS1 and BSS2)includes one or more stations STA1, STA2, STA3, STA4, and STA5, accesspoints PCP/AP-1 and PCP/AP-2 which are stations providing a distributionservice, and a distribution system (DS) connecting the multiple accesspoints PCP/AP-1 and PCP/AP-2.

The station (STA) is a predetermined device including medium accesscontrol (MAC) following a regulation of an IEEE 802.11 standard and aphysical layer interface for a radio medium, and includes both anon-access point (non-AP) station and an access point (AP) in a broadsense. Further, in the present specification, a term ‘terminal’ may beused to refer to a concept including a wireless LAN communication devicesuch as non-AP STA, or an AP, or both terms. A station for wirelesscommunication includes a processor and a transceiver and according tothe embodiment, may further include a user interface unit and a displayunit. The processor may generate a frame to be transmitted through awireless network or process a frame received through the wirelessnetwork and besides, perform various processing for controlling thestation. In addition, the transceiver is functionally connected with theprocessor and transmits and receives frames through the wireless networkfor the station.

The access point (AP) is an entity that provides access to thedistribution system (DS) via wireless medium for the station associatedtherewith. In the infrastructure BSS, communication among non-APstations is, in principle, performed via the AP, but when a direct linkis configured, direct communication is enabled even among the non-APstations. Meanwhile, in the present invention, the AP is used as aconcept including a personal BSS coordination point (PCP) and mayinclude concepts including a centralized controller, a base station(BS), a node-B, a base transceiver system (BTS), and a site controllerin a broad sense.

A plurality of infrastructure BSSs may be connected with each otherthrough the distribution system (DS). In this case, a plurality of BSSsconnected through the distribution system is referred to as an extendedservice set (ESS).

FIG. 2 illustrates an independent BSS which is a wireless LAN systemaccording to another embodiment of the present invention. In theembodiment of FIG. 2, duplicative description of parts, which are thesame as or correspond to the embodiment of FIG. 1, will be omitted.

Since a BSS3 illustrated in FIG. 2 is the independent BSS and does notinclude the AP, all stations STA6 and STA7 are not connected with theAP. The independent BSS is not permitted to access the distributionsystem and forms a self-contained network. In the independent BSS, therespective stations STA6 and STA7 may be directly connected with eachother.

FIG. 3 is a block diagram illustrating a configuration of a station 100according to an embodiment of the present invention.

As illustrated in FIG. 3, the station 100 according to the embodiment ofthe present invention may include a processor 110, a transceiver 120, auser interface unit 140, a display unit 150, and a memory 160.

First, the transceiver 120 transmits and receives a radio signal such asa wireless LAN packet, or the like and may be embedded in the station100 or provided as an exterior. According to the embodiment, thetransceiver 120 may include at least one transmit/receive module usingdifferent frequency bands. For example, the transceiver 120 may includetransmit/receive modules having different frequency bands such as 2.4GHz, 5 GHz, and 60 GHz. According to an embodiment, the station 100 mayinclude a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the AP or an external station according to a wirelessLAN standard of a frequency band supported by the correspondingtransmit/receive module. The transceiver 120 may operate only onetransmit/receive module at a time or simultaneously operate multipletransmit/receive modules together according to the performance andrequirements of the station 100. When the station 100 includes aplurality of transmit/receive modules, each transmit/receive module maybe implemented by independent elements or a plurality of modules may beintegrated into one chip.

Next, the user interface unit 140 includes various types of input/outputmeans provided in the station 100. That is, the user interface unit 140may receive a user input by using various input means and the processor110 may control the station 100 based on the received user input.Further, the user interface unit 140 may perform output based on acommand of the processor 110 by using various output means.

Next, the display unit 150 outputs an image on a display screen. Thedisplay unit 150 may output various display objects such as contentsexecuted by the processor 110 or a user interface based on a controlcommand of the processor 110, and the like. Further, the memory 160stores a control program used in the station 100 and various resultingdata. The control program may include an access program required for thestation 100 to access the AP or the external station.

The processor 110 of the present invention may execute various commandsor programs and process data in the station 100. Further, the processor110 may control the respective units of the station 100 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 110 may execute the program foraccessing the AP stored in the memory 160 and receive a communicationconfiguration message transmitted by the AP. Further, the processor 110may read information on a priority condition of the station 100 includedin the communication configuration message and request the access to theAP based on the information on the priority condition of the station100. The processor 110 of the present invention may represent a maincontrol unit of the station 100 and according to the embodiment, theprocessor 110 may represent a control unit for individually controllingsome component of the station 100, for example, the transceiver 120, andthe like. The processor 110 controls various operations of radio signaltransmission/reception of the station 100 according to the embodiment ofthe present invention. A detailed embodiment thereof will be describedbelow.

The station 100 illustrated in FIG. 3 is a block diagram according to anembodiment of the present invention, where separate blocks areillustrated as logically distinguished elements of the device.Accordingly, the elements of the device may be mounted in a single chipor multiple chips depending on design of the device. For example, theprocessor 110 and the transceiver 120 may be implemented while beingintegrated into a single chip or implemented as a separate chip.Further, in the embodiment of the present invention, some components ofthe station 100, for example, the user interface unit 140 and thedisplay unit 150 may be optionally provided in the station 100.

FIG. 4 is a block diagram illustrating a configuration of an AP 200according to an embodiment of the present invention.

As illustrated in FIG. 4, the AP 200 according to the embodiment of thepresent invention may include a processor 210, a transceiver 220, and amemory 260. In FIG. 4, among the components of the AP 200, duplicativedescription of parts which are the same as or correspond to thecomponents of the station 100 of FIG. 2 will be omitted.

Referring to FIG. 4, the AP 200 according to the present inventionincludes the transceiver 220 for operating the BSS in at least onefrequency band. As described in the embodiment of FIG. 3, thetransceiver 220 of the AP 200 may also include a plurality oftransmit/receive modules using different frequency bands. That is, theAP 200 according to the embodiment of the present invention may includetwo or more transmit/receive modules among different frequency bands,for example, 2.4 GHz, 5 GHz, and 60 GHz together. Preferably, the AP 200may include a transmit/receive module using a frequency band of 6 GHz ormore and a transmit/receive module using a frequency band of 6 GHz orless. The respective transmit/receive modules may perform wirelesscommunication with the station according to a wireless LAN standard of afrequency band supported by the corresponding transmit/receive module.The transceiver 220 may operate only one transmit/receive module at atime or simultaneously operate multiple transmit/receive modulestogether according to the performance and requirements of the AP 200.

Next, the memory 260 stores a control program used in the AP 200 andvarious resulting data. The control program may include an accessprogram for managing the access of the station. Further, the processor210 may control the respective units of the AP 200 and control datatransmission/reception among the units. According to the embodiment ofthe present invention, the processor 210 may execute the program foraccessing the station stored in the memory 260 and transmitcommunication configuration messages for one or more stations. In thiscase, the communication configuration messages may include informationabout access priority conditions of the respective stations. Further,the processor 210 performs an access configuration according to anaccess request of the station. The processor 210 controls variousoperations such as radio signal transmission/reception of the AP 200according to the embodiment of the present invention. A detailedembodiment thereof will be described below.

FIG. 5 is a diagram schematically illustrating a process in which a STAsets a link with an AP.

Referring to FIG. 5, the link between the STA 100 and the AP 200 is setthrough three steps of scanning, authentication, and association in abroad way. First, the scanning step is a step in which the STA 100obtains access information of BSS operated by the AP 200. A method forperforming the scanning includes a passive scanning method in which theAP 200 obtains information by using a beacon message (S101) which isperiodically transmitted and an active scanning method in which the STA100 transmits a probe request to the AP (S103) and obtains accessinformation by receiving a probe response from the AP (S105).

The STA 100 that successfully receives wireless access information inthe scanning step performs the authentication step by transmitting anauthentication request (S107 a) and receiving an authentication responsefrom the AP 200 (S107 b). After the authentication step is performed,the STA 100 performs the association step by transmitting an associationrequest (S109 a) and receiving an association response from the AP 200(S109 b).

Meanwhile, an 802.1X based authentication step (S111) and an IP addressobtaining step (S113) through DHCP may be additionally performed. InFIG. 5, the authentication server 300 is a server that processes 802.1Xbased authentication with the STA 100 and may be present in physicalassociation with the AP 200 or present as a separate server.

When using Orthogonal Frequency Division Multiple Access (OFDMA) totransmit data, any one wireless communication terminal may transmit datasimultaneously to a plurality of wireless communication terminals. Also,any one wireless communication terminal may simultaneously receive datafrom a plurality of wireless communication terminals. For this, afrequency channel is allocated to a plurality of wireless communicationterminals that communicate with any one wireless communication terminal.Therefore, it is necessary for any one wireless communication terminalto efficiently signal a plurality of wireless communication terminals ofinformation of a frequency channel allocated to each of the plurality ofwireless communication terminals. An embodiment of the present inventionin which any one wireless communication terminal efficiently signalsinformation of a frequency channel allocated to each of a plurality ofwireless communication terminals to the plurality of wirelesscommunication terminals will be described with reference to the drawingsfollowing FIG. 5. For convenience of description, any one wirelesscommunication terminal that communicates simultaneously with a pluralityof wireless communication terminals is referred to as a first wirelesscommunication terminal and a plurality of wireless communicationterminals that simultaneously communicate with the first wirelesscommunication terminal are referred to as a plurality of second wirelesscommunication terminals. At this time, the first wireless communicationterminal may be the access point 200. In addition, the second wirelesscommunication terminal may be the station 100 associated with the accesspoint 200. According to a specific embodiment, the first wirelesscommunication terminal may be referred to as a base wirelesscommunication terminal.

In addition, the first wireless communication terminal may be a wirelesscommunication terminal that serves as a cell coordinator for allocatinga communication medium resource and performing scheduling incommunication with a plurality of wireless communication terminals.

In a specific embodiment, the first wireless communication terminal maybe a wireless communication terminal that allocates a communicationmedium resource and performs scheduling in an independent network, suchas an ad-hoc network, which is not connected to an external distributionservice.

In addition, the first wireless communication terminal may be at leastone of a base station, an eNB, and a transmission point TP. A frameincluding information of a frequency channel allocated to each of aplurality of second wireless communication terminals according to anembodiment of the present invention will be described with reference toFIGS. 6 to 8. A frame including information of a frequency channelallocated to each of a plurality of second wireless communicationterminals is referred to as a poll frame. According to a specificembodiment, the poll frame may be referred to as a trigger frame. In aspecific embodiment, the first wireless communication terminal maytransmit a poll frame to the second wireless communication terminal tosignal the second wireless communication terminal of information of afrequency channel allocated to the second wireless communicationterminal. Also, after transmitting a poll frame, the first wirelesscommunication terminal may transmit data to the plurality of secondwireless communication terminals simultaneously through a channelallocated to each of the plurality of second wireless terminals. Also,after receiving the poll frame, the second wireless communicationterminal may transmit data to the first wireless communication terminalsimultaneously with the other second wireless communication terminals.

FIG. 6 is a view illustrating a structure of a poll frame according toan embodiment of the present invention.

The poll frame may include a Basic Service Set Identifier (BSSID) foridentifying a basic service set in which the poll frame is transmitted.At this time, the BSSID may indicate the MAC address of the firstwireless communication terminal transmitting the poll frame.

The poll frame may include source address information indicating theaddress of the first wireless communication terminal transmitting thepoll frame. At this time, the address of the first wirelesscommunication terminal may be the MAC address of the first wirelesscommunication terminal. The BSSID and the source address information maybe identically used as information indicating the first wirelesscommunication terminal. Accordingly, according to a specific embodiment,the poll frame may include any one of the BSSID and the source addressinformation.

The poll frame may include length information indicating the length ofthe poll frame. The second wireless communication terminal may obtainthe number of the second wireless communication terminals participatingin the data transmission based on the length information. Specifically,the second wireless communication terminal obtains a variable length bysubtracting the length of the fixed field of the poll frame, which isfixed regardless of the number of the second wireless communicationterminals participating in the data transmission, from the length of thepoll frame indicated by the length information. Then, the secondwireless communication terminal may divide the obtained variable lengthby the length of the variable field required for one second wirelesscommunication terminal, thereby obtaining the number of the secondwireless communication terminals participating in the data transmission.

The poll frame may include channel vector information indicatinginformation of a frequency channel allocated to the second wirelesscommunication terminal. The channel vector information may include afrequency channel allocated to the second wireless communicationterminal. In addition, the channel vector information may includedestination address information indicating the address of the secondwireless communication terminal to which the corresponding channel isallocated. At this time, the information indicating the address of thesecond wireless communication terminal may be an association identifier(AID) for identifying the association between the first wirelesscommunication terminal and the second wireless communication terminal.The second wireless communication terminal may recognize the channelallocated to the second wireless communication terminal based on thechannel vector information, and receive data from the first wirelesscommunication terminal through the corresponding channel. The secondwireless communication terminal may recognize the channel allocated tothe second wireless communication terminal based on the channel vectorinformation, and transmit data to the first wireless communicationterminal through the corresponding channel. The specific format ofconcrete channel vector information will be described later withreference to FIGS. 8 to 17.

In a specific embodiment, the poll frame may have the same structure asthat of the embodiment of FIG. 6. Specifically, the poll frame mayinclude a frame control field indicating the control information of aframe. The poll frame may include a BSSID field indicating a BSSID. Thepoll frame may include a source address (SA) field indicating sourceaddress information. The poll frame may include a length fieldindicating length information. The poll frame may include a CH vectorfield indicating channel vector information. The poll frame may includean STA ID field indicating the address of a second wirelesscommunication terminal to which a channel indicated by the CH vectorfield is allocated. The poll frame may include an FCS field including acyclical redundancy check (CRC) value for error detection.

FIG. 7 is a view illustrating a structure of a poll frame according toanother embodiment of the present invention.

The poll frame may include duration information indicating a timerequired for data transmission after poll frame transmission. Throughthis, it is possible to prevent other wireless communication terminalsfrom accessing a frequency channel used for data transmission before thedata transmission is terminated.

In addition, the poll frame may include information indicating thenumber of second wireless communication terminals to which the pollframe allocates a frequency channel.

In a specific embodiment, the poll frame may have the same structure asthat of the embodiment of FIG. 7. Specifically, the poll frame mayinclude a duration field indicating duration information. Also,depending on a specific situation, the duration field may indicate thenumber of second wireless communication terminals to which the pollframe allocates a frequency channel. Also, depending on a specificsituation, the duration field may indicate length information of thepoll frame.

As described above, when a first wireless communication terminal and aplurality of second wireless communication terminals communicate usingthe OFDMA, it is necessary to signal the plurality of second wirelesscommunication terminals of channel information allocated to each of theplurality of second wireless communication terminals. For this, the pollframe may include channel vector information indicating information of afrequency channel allocated to the second wireless communicationterminal. Such channel vector information may be used to indicateinformation of a channel allocated to the second wireless communicationterminal even in a frame other than the poll frame or the preamble of asignal including a frame. An embodiment in which the specific format ofchannel vector information and the channel vector information are usedwill be described with reference to FIGS. 8 to 17.

FIG. 8 is a view illustrating a structure of a CH vector field in a pollframe according to an embodiment of the present invention.

As OFDMA transmission becomes available, a plurality of second wirelesscommunication terminals according to an embodiment of the presentinvention may divide the minimum unit frequency bandwidth that a firstwireless communication terminal uses in communication and communicatewith the first wireless communication terminal at the same time by usingeach divided bandwidth. At this time, the minimum unit frequencybandwidth may be 20 MHz. Therefore, the channel vector information mayinclude sub-channel information as well as channel information. At thistime, the channel information is information on a channel having abandwidth greater than the minimum unit frequency bandwidth. Thesub-channel information, as a sub-band included in a channel, isinformation on a sub-channel having a bandwidth less than the minimumunit frequency bandwidth. At this time, a channel usage patternavailable for the first wireless communication terminal and the secondwireless communication terminal may be predefined. In this case, achannel other than the predetermined channel usage pattern may not beused. At this time, the channel usage pattern may indicate whether therange of a frequency band and the frequency band are combined. Such achannel usage pattern may be set for various regulations and technicalfeasibility. Also, such a channel usage pattern may be represented by anindex. Therefore, the channel vector information may include indexinformation indicating a channel usage pattern. Specifically, thechannel vector information may include channel index information. Andthe channel vector information may include sub-channel index informationindicating a sub-channel.

In addition, in order to prevent the size of a poll frame from becominglarge as the size of the channel vector information becomes too large,the channel vector information may include channel allocationinformation on a predetermined number of the second wirelesscommunication terminals. Specifically, when it is necessary to transmitchannel allocation information to second wireless communicationterminals of more than a predetermined number, the first wirelesscommunication terminal may divide channel allocation information for theplurality of second wireless communication terminals into a plurality ofpoll frames and transmit the plurality of poll frames.

In addition, in order to prevent the size of a poll frame from becominglarge as the size of the channel vector information becomes too large,the channel vector information may include channel information by asecond wireless communication terminal group unit including a pluralityof second wireless communication terminals instead of a second wirelesscommunication terminal unit. Specifically, the channel vectorinformation may include a group identifier for identifying the group ofa second wireless communication terminal and channel informationallocated to the group of the second wireless communication terminal. Atthis time, the first wireless communication terminal may manage thegroup identifier. Specifically, the first wireless communicationterminal may assign a group identifier to a plurality of second wirelesscommunication terminals in an association or a re-association process.At this time, the first wireless communication terminal may allocate areserve group identifier remaining for future use to the second wirelesscommunication terminal. In addition, the maximum number of groupidentifiers that the first wireless communication terminal allocates maybe limited to a predetermined number. When the channel vectorinformation includes channel allocation information by each group unitof the second wireless communication terminal, the first wirelesscommunication terminal may signal channel information allocated to eachsecond wireless communication terminal included in a group through thechannel vector information in the preamble of data.

In a specific embodiment, the channel vector information includesinformation for identifying the second wireless communication terminaland channel information allocated to the second wireless communicationterminal. At this time, the channel information may include channelindex information and sub-channel index information as described above.Specifically, the channel information may be a 2-byte field as in theembodiment of FIG. 8. In addition, the channel vector informationindicates channel index information through 12 bits and sub-channelindex information through 4 bits. When the first wireless communicationterminal uses a frequency hand in which a plurality of minimum unitfrequency bands are combined, a field indicating such sub-channel indexinformation may not be used. Specifically, when the size of the minimumunit frequency band is 20 MHz and the first wireless communicationterminal uses a frequency band of greater than 20 MHz, the firstwireless communication terminal and the second wireless communicationterminal may not use the sub-channel index information. In addition,some of the 12 bits indicating the channel index information may be leftas reserved bits in preparation for the format change of the channelvector information.

As described above, the poll frame may include a duration fieldindicating duration information. Also, depending on a specificsituation, the duration field may indicate the number of second wirelesscommunication terminals to which the poll frame allocates a frequencychannel. Also, depending on a specific situation, the duration field maybe information indicating the number of second wireless communicationterminals to which the poll frame allocates a channel. At this time, thesecond wireless communication terminal may determine the length of thepoll frame based on the duration field. This is because the length ofthe poll frame becomes longer as the number of second wirelesscommunication terminals allocating a channel becomes larger.

FIG. 9 is a view illustrating a channel index of a 5 GHz frequency bandaccording to an embodiment of the present invention, and FIG. 10 is aview illustrating a channel index of a 5 GHz frequency band according toanother embodiment of the present invention.

When the first wireless communication terminal uses only a combinationof contiguous frequency bands, the same channel index as in theembodiment of FIG. 9 may be used. In such a case, the number ofcontiguous frequency channels is 256 or less. Therefore, a field forindicating the channel index information in the channel vectorinformation may be a field of 8 bits or less.

In a specific embodiment, the first wireless communication terminal andthe second wireless communication terminal may use a combination ofnon-contiguous frequency bands. In such a case, the same channel indexas in the embodiment of FIG. 10 may be used. For example, the channelindex 800 in FIG. 10 (c) represents a frequency band combining thefrequency hands indicated by each of the channel index 4 and the channelindex 24, which are not contiguous to each other. At this time, thenumber of available channels may be 256 or more. In such a case, a fieldfor indicating the channel index information in the channel vectorinformation may be a field of 8 bits or more. Specifically, the sum ofthe size of a field indicating channel index information and the size ofa field indicating sub-channel index information may be 16 bits.Specifically, the field for indicating the channel index information maybe a 12-bit field. Also, the first wireless communication terminal andthe second wireless communication terminal may use a bandwidth that isnot one, two, four, or eight times the minimum unit frequency bandwidth.For example, in the embodiment of FIG. 10 (b) in which a minimum unitfrequency bandwidth is 20 MHz, the frequency band indicated by thechannel index 240 has a 100 MHz bandwidth that is five times the minimumunit frequency bandwidth of 20 MHz. Also, the first wirelesscommunication terminal and the second wireless communication terminalmay use frequency bands that is adjacent but is not utilizedsimultaneously in 802.11ac. For example, the channel index 75 in FIG. 10(a) represents a frequency band combining the frequency bands indicatedby each of the channel index 10 and the channel index 75.

As described above, the channel vector information may includesub-channel index information. At this time, the sub-channel indexinformation may indicate sub-channel or sub-carrier allocation. Inaddition, the channel vector information including the sub-channel indexinformation may be included in the preamble of a communication signalbetween the first wireless communication terminal and the secondwireless communication terminal as well as the poll frame. Suchsub-channel index information will be described with reference to FIGS.11 to 18.

FIG. 11 is a view illustrating a sub-channel index in a frequency bandof 20 MHz according to an embodiment of the present invention.

In a specific embodiment, the first wireless communication terminal andthe second wireless communication terminal may divide a frequency bandhaving a minimum unit frequency bandwidth into eight sub-bands. At thistime, the first wireless communication terminal and the second wirelesscommunication terminal may use a combination of eight sub-hands as asub-channel. The minimum unit frequency bandwidth may be 20 MHz. Thefirst wireless communication terminal and the second wirelesscommunication terminal may use the fifteen sub-channels as shown in FIG.11 by combining eight sub-bands with adjacent sub-bands. In addition,when the first wireless communication terminal and the second wirelesscommunication terminal indicate the channel vector information by usingthe group identifier, the sub-channel index should represent the casethat the second wireless communication terminal is included in thecorresponding group but does not receive a sub-channel. Therefore, thenumber of cases that the sub-channel index should express is 16 intotal. Therefore, the sub-channel index may be represented by a 4-bitfield.

FIG. 12 is a view illustrating a sub-channel index in a frequency bandof 20 MHz according to another embodiment of the present invention.

In a specific embodiment, the first wireless communication terminal andthe second wireless communication terminal may divide a frequency handhaving a minimum unit frequency bandwidth into nine sub-bands. Theminimum unit frequency bandwidth may be 20 MHz. The first wirelesscommunication terminal and the second wireless communication terminalmay use the fifteen sub-channels as shown in FIG. 12 by combining eightsub-bands with adjacent sub-bands except for the fifth frequencysub-band. Except when all the minimum unit frequency bands are used, ifthe case that channel vector information is indicated using a groupidentifier is included, the total number of sub-channels is 15. Inaddition, the sub-channel index should cover the case that the secondwireless communication terminal is included in the corresponding groupbut does not receive a sub-channel. Therefore, the number of cases thatthe sub-channel index should display is 16 in total. Therefore, thesub-channel index may be represented by a 4-bit field.

FIG. 13 is a view illustrating a sub-channel index in a frequency bandof 20 MHz including a combination of non-contiguous sub-bands accordingto another embodiment of the present invention.

In a specific embodiment, the first wireless communication terminal andthe second wireless communication terminal may divide a frequency bandhaving a minimum unit frequency bandwidth into nine sub-bands. Theminimum unit frequency bandwidth may be 20 MHz. The first wirelesscommunication terminal and the second wireless communication terminalmay combine the nine sub-bands without restriction and use them as asub-channel. Specifically, the first wireless communication terminal andthe second wireless communication terminal may combine non-continuoussub-bands and use them as one sub-channel. For example, as shown in FIG.13, the sub-channel index 17 represents a frequency band obtained bycombining frequency bands indicated by the sub-channel index 1, thesub-channel index 2, and the sub-channel index 5. In such a case, sincethe number of cases that a sub-channel index should represent is 16 ormore, the sub-channel index may be represented by a field of 5 bits ormore.

The preamble of a signal transmitted from the first wirelesscommunication terminal to the second wireless communication terminal mayinclude sub-channel or sub-carrier allocation information. In a specificembodiment, the preamble of a signal transmitted from the first wirelesscommunication terminal to the second wireless communication terminal mayinclude sub-channel index information. Through this, the second wirelesscommunication terminal may decode the preamble signal transmitted fromthe first wireless communication terminal and obtain information on thesub-channel allocated to the second wireless communication terminal. Ina specific embodiment, the preamble of a signal transmitted from thefirst wireless communication terminal to the second wirelesscommunication terminal may include sub-channel index information in atleast one of SIG-A, SIG-B, and SIG-C. The specific format of sub-channelinformation included in the preamble of a signal transmitted from thefirst wireless communication terminal to the second wirelesscommunication terminal will be described with reference to FIGS. 14 to18.

FIG. 14 is a view illustrating a preamble including sub-channelinformation according to an embodiment of the present invention.

As described above, the channel vector information included in the pollframe may include channel allocation information by each group unit ofthe second wireless communication terminal including a plurality ofsecond wireless communication terminals, instead of the second wirelesscommunication terminal unit. At this time, the sub-channel informationincluded in the preamble of a signal transmitted from the first wirelesscommunication terminal to the second wireless communication terminal mayinclude the group identifier of a group including the second wirelesscommunication terminal to which the sub-channel is allocated.

In addition, the sub-channel information may include informationindicating a sub-channel allocated to the second wireless communicationterminal. At this time, the information indicating the sub-channel maybe a sub-channel index indicating the sub-channel.

In a specific embodiment, the format of the sub-channel informationincluded in the preamble may be one as shown in FIG. 14. Specifically,the sub-channel information may include a Group ID field indicating agroup identifier. In a specific embodiment, the Group ID field may be afield of 6 bits or more. For example, when the maximum number of secondwireless communication terminals connected to one first wirelesscommunication terminal is 4, the Group ID field may be a 6-bit field. Inaddition, when the maximum number of second wireless communicationterminals connected to one first wireless communication terminal is morethan 4, the Group ID field may be a field of more than 6 bits.

In addition, the sub-channel information may include a CH vector fieldindicating a sub-channel allocated to the second wireless communicationterminal. In a specific embodiment, the CH vector field may indicatethat no sub-channel is allocated to the second wireless communicationterminal corresponding to the CH vector field. In such a case, the valueof the CH vector field corresponding to the second wirelesscommunication terminal not participating in the transmission with thefirst wireless communication may be zero. In a specific embodiment, theCH vector field may be a 4-bit field. At present, Multi User-Multi Inputand Multi Output (MU-MIMO) allows the simultaneous connection of a totalof four wireless communication terminals to the first wirelesscommunication terminal. Thus, the sub-channel information may includefour CH vector fields. In addition, when the number of second wirelesscommunication terminals that simultaneously access the first wirelesscommunication terminal allowed by MU-MIMO is increased, the number ofthe CH vector fields may be increased

In addition, the order of the second wireless communication terminalcorresponding to the CH vector field may follow the order of the secondwireless communication terminal identifier in the channel vectorinformation included in the above-described poll frame. Therefore, thesecond wireless communication terminal may obtain the sub-channelinformation corresponding to the second wireless communication terminalitself based on the order of the second wireless communication terminalidentifier of the channel vector information included in the poll frame.

FIG. 15 is a view illustrating a preamble including sub-channelinformation according to another embodiment of the present invention.

In preparation for the case that the number of second wirelesscommunication terminals connected to one first wireless communicationterminal at the same time is increased, the number of CH vector fieldsmay not be limited as shown in FIG. 15.

FIG. 16 is a view illustrating a preamble including sub-channelinformation according to another embodiment of the present invention.

As described with reference to FIG. 15, when the number of CH vectorfields is not limited, the second wireless communication terminal has tocontinuously decode a variable signal without knowing the number of CHvector fields. To solve this problem, the sub-channel information of thepreamble included in a signal transmitted from the first wirelesscommunication terminal to the second wireless communication terminal mayinclude information indicating the number of the second wirelesscommunication terminals to which the sub-channel is allocated. Inanother specific embodiment, if one second wireless communicationterminal is allocated per one sub-channel, the sub-channel informationmay include the number of allocated sub-channels.

In a specific embodiment, the sub-channel information may include aNumber of User field indicating the number of second wirelesscommunication terminals to which a sub-channel is allocated, as in theembodiment of FIG. 16. At this time, the Number of User field may be a4-bit field.

In another specific embodiment, the sub-channel information may includea Channel divide factor field indicating the number of allocatedsub-channels, as in the embodiment of FIG. 16. At this time, the Channeldivide factor field may be a 4-bit field.

Through such an embodiment, the second wireless communication terminalmay accurately recognize the size of a preamble to be decoded.

FIG. 17 is a view illustrating a preamble including sub-channelinformation according to another embodiment of the present invention.

According to the above-described embodiment, even if a sub-channel isnot allocated, the second wireless communication terminal should decodeall the sub-channel information to determine whether the sub-channel isallocated. In order to prevent this, the sub-channel informationincluded in the preamble of a signal transmitted from the first wirelesscommunication terminal to the second wireless communication terminal mayinclude information indicating whether the OFDMA communication using thesub-channel is used or not.

In a specific embodiment, the sub-channel information may include anOFDMA Indication field indicating whether to use OFDMA communicationusing a sub-channel, as in the embodiment of FIG. 17. In a specificembodiment, the OFDMA Indication field may be a 1-bit flag. For example,if the value of the OFDMA Indication field is 1, the OFDMA Indicationfield may indicate that the first wireless communication terminalallocates a sub-channel to the second wireless communication terminalfor OFDMA communication using the sub-channel.

When the OFDMA Indication field is a 1-bit flag, the Number of Userfield described above may be a 3-bit field. Also, if the value indicatedby the Number of User field is N, it may indicate that a sub-channel isallocated to the N−2 second wireless communication terminal. The reasonwhy the sub-channel is allocated to the N−2 second wirelesscommunication terminals instead of the N second wireless communicationterminals is that the sub channel is allocated to two or more secondwireless communication terminals when OFDMA communication using thesub-channel is used.

FIG. 18 is a view illustrating a CH vector field indicating acombination of non-contiguous sub-band channels according to anotherembodiment of the present invention.

In the above-described specific embodiment, it is described that the CHvector field included in the sub-channel information may be 4 bits.However, when a sub-channel indicating a combination of non-contiguoussub-bands is supported, the number of sub-channels is increased, so thatthe CH vector field may be a field of 5 bits or more.

In a specific embodiment, the channel vector information may indicatethat the second wireless communication terminal randomly accesses withina predetermined channel range. At this time, the second wirelesscommunication terminal may attempt to access randomly within a specifiedchannel range. If the second wireless communication terminal fails intransmission due to a collision with another wireless communicationterminal at the time of random access, the second wireless communicationterminal may try to access again.

It is described with reference to FIGS. 6 to 18 that frequency channelinformation allocated to each of the plurality of second wirelesscommunication terminals is signaled for OFDMA communication between thefirst wireless communication terminal and the plurality of secondwireless communication terminals. It is described with reference toFIGS. 19 to 30 that the first wireless communication terminal transmitsdata to the plurality of second wireless communication terminals at thesame time.

When a wireless communication terminal performs one-to-onecommunication, it guarantees a Transmit Opportunity (TXOP) using a ReadyTo Send (RTS) frame indicating that it is ready for transmission and aClear To Send (CTS) frame indicating that it is ready for reception.However, since the legacy RTS frame and the CTS frame are for one-to-onecommunication, a wireless communication terminal for transmitting dataand a wireless communication terminal for receiving the data are limitedto one. Therefore, there is a need for a new TXOP reserving method for acase in which any one wireless communication terminal simultaneouslytransmits data to a plurality of wireless communication terminals usingOFDMA. This will be described with reference to FIGS. 19 to 29.

FIG. 19 is a view illustrating a structure of an RTS-to-Self frameaccording to an embodiment of the present invention.

A first wireless communication terminal may transmit a frame fornotifying a plurality of second wireless communication terminals that atransmission to the plurality of second wireless communication terminalsstarts. At this time, a frame for notifying that a transmission to aplurality of second wireless communication terminals starts may bemodified by using an RTS frame.

The RTS frame includes a frame control field indicating information onframe control, a duration field indicating a value for updating a valueof a network allocation vector (NAV), an RA field indicating the addressof a wireless communication terminal that receives data, a TA fieldindicating the address of a wireless communication terminal thattransmits data, and an FCS field including a cyclic redundancy check(CRC) value for error detection.

In order to notify that the transmission to the plurality of secondwireless communication terminals starts, the first wirelesscommunication terminal may set the value of the RA field and the valueof the TA field in the RTS frame to its own address. For convenience ofdescription, the RTS frame set in this manner is referred to as anRTS-to-Self frame. The first wireless communication terminal maytransmit the RTS-to-Self frame through a plurality of channels.Specifically, the first wireless communication terminal may transmit theRTS-to-Self frame to the plurality of second wireless communicationterminals in a BSS through a plurality of channels. Also, the firstwireless communication terminal may set the value of the duration fieldbased on the transmission time of the RTS-to-Self frame and the datatransmission time for the plurality of second wireless communicationterminals. Specifically, the first wireless communication terminal mayset the value of the duration field to the sum of the transmission timeof an RTS-to-Self frame, a short inter-frame space (SIFS) defined in the802.11 standard, the transmission time of a poll frame, an SIFS, thetransmission time of a CTS frame, an SIFS, a data transmission time, anSIFS, and the transmission time of an ACK frame.

At this time, when receiving the RTS-to-Self frame, a wirelesscommunication terminal supporting an embodiment of the present inventionreceives a signal transmitted by the second wireless communicationterminal until channel allocation information is checked. Also, awireless communication terminal that does not support an embodiment ofthe present invention stops accessing to a channel and waits due to theduration field value of the RTS-to-Self frame. Accordingly, the firstwireless communication terminal may secure a TXOP from both a wirelesscommunication terminal supporting an embodiment of the present inventionand a wireless communication terminal not supporting an embodiment ofthe present invention through the RTS-to-Self frame. A specificoperation in which the first wireless communication terminal transmitsdata to the plurality of second wireless communication terminals usingthe RTS-to-Self frame will be described with reference to FIGS. 20 to29.

FIG. 20 is a view illustrating that an access point according to anembodiment of the present invention simultaneously transmits data to aplurality of stations using an RTS-to-Self frame.

If a channel is in an idle state for a predetermined time, the firstwireless communication terminal transmits an RTS-to-Self frame to aplurality of channels after waiting for a random value within acontention window value. Specifically, if a channel is in an idle statefor a predetermined time, the first wireless communication terminaltransmits an RTS-to-Self frame to a plurality of wireless communicationterminals in a BSS after waiting for a random value within a contentionwindow value. At this time, the first wireless communication terminalmay transmit an RTS-to-Self frame to a plurality of idle channels otherthan a busy channel being currently used by another user. At this point,the predetermined time may be an Arbitration Inter-Frame Space (AIFS) ora Distributed Inter-Frame Space (DIFS) defined by the 802.11 standard.

The first wireless communication terminal transmits the above-describedpoll frame to the plurality of second wireless communication terminals.Specifically, the first wireless communication terminal may transmit theabove-described poll frame to the plurality of second wirelesscommunication terminals through one channel. In a specific embodiment,the first wireless communication terminal may transmit theabove-described poll frame through a primary channel Primary CH after apredetermined time. At this time, the first wireless communicationterminal may transmit a poll frame after a predetermined time. Thepredetermined time may be an SIFS.

The plurality of second wireless communication terminals receiving thepoll frame obtain the channel vector information from the poll frame.Through this, the plurality of second wireless communication terminalsmay recognize the channel allocated to the plurality of second wirelesscommunication terminals. In addition, as described above, the secondwireless communication terminal may obtain the channel vectorinformation based on the preamble of a communication signal.

The plurality of second wireless communication terminals transmit a CTSframe to the first wireless communication terminal based on the obtainedchannel vector information. Specifically, the plurality of secondwireless communication terminals transmit the CTS frame through achannel allocated to each of the plurality of second wirelesscommunication terminals. Specifically, after a predetermined time fromthe poll frame transmission, the plurality of second wirelesscommunication terminals may transmit a CTS frame to the first wirelesscommunication terminal. At this point, the predetermined time may be anSIFS.

The first wireless communication terminal transmits data to theplurality of second wireless communication terminals that transmit theCTS frame. Specifically, after a predetermined time from the CTS frametransmission, the first wireless communication terminal may transmitdata to the plurality of second wireless communication terminals thattransmit the CTS frame. At this point, the predetermined time may be anSIFS. Specifically, the first wireless communication terminal maytransmit data to the plurality of second wireless communicationterminals through a channel allocated to each of the plurality of secondwireless communication terminals. The plurality of second wirelesscommunication terminals that receive the data transmit the ACK frame tothe first wireless communication terminal. Specifically, after apredetermined time, the plurality of second wireless communicationterminals that receive the data may transmit the ACK frame to the firstwireless communication terminal. At this point, the predetermined timemay be an SIFS.

The first wireless communication terminal may simultaneously transmitdata to the plurality of second wireless communication terminals usingOFDMA. However, a frequency channel that the first wirelesscommunication may use is limited. Therefore, the first wirelesscommunication should efficiently allocate an available frequency channeland transmit the data. In addition, the size of data that the firstwireless communication terminal transmits to the plurality of secondwireless communication terminals at the same time may be all different.Therefore, it may be inefficient to allocate frequency channels of thesame size to all the second wireless communication terminals. When thefirst wireless communication terminal aggregates data to be transmittedto the plurality of second wireless communication terminals andtransmits the aggregated data to the plurality of second wirelesscommunication terminals at the same time by using all availablefrequency channels, it may use an available frequency without waste.Additionally, in such a case, the first wireless communication terminalis not required to perform a complicated operation for allocating achannel to each second wireless communication terminal. Accordingly, adata transmission method through an aggregate-MAC protocol data unitwhere a plurality of MAC protocol data units including data to betransmitted to a plurality of second wireless communication terminalsare aggregated is required. At this point, an aggregate-MAC protocoldata unit for transmitting data to a plurality of second wirelesscommunication terminals at the same time is different from a legacyaggregate-MAC protocol data unit (A-MPDU) that aggregates MPDUs to betransmitted to the same address and transmits the MPDUs. Accordingly, anaggregate-MAC protocol data unit for transmitting data to a plurality ofsecond wireless communication terminals at the same time is referred toas plural terminal A-MPDUs or plural station A-MPDUs.

Also, the first wireless communication terminal may transmit the headersof plural terminal A-MPDUs, which respectively correspond to theplurality of second wireless communication terminals, to the pluralityof second wireless communication terminals through a channel allocatedto each of the plurality of second wireless communication terminals. Theheader signals information in the plural terminal A-MPDUs. Inparticular, the header may include the address of the second wirelesscommunication terminal corresponding to the header. In addition, theheader may include information indicating a position of datacorresponding to each of the plurality of second wireless communicationterminals. For convenience of description, this information is referredto as start point vector information. The start point vector informationmay include at least one of a time and a channel through which thesecond wireless communication terminal receives data. Also, the startpoint vector information may be located after the legacy MPDU header. Insuch a case, a wireless communication terminal not supporting anembodiment of the present invention treats the header like a payload.Also, a wireless communication terminal not supporting an embodiment ofthe present invention may know that another wireless communicationterminal is using the corresponding channel through the header. And, awireless communication terminal not supporting an embodiment of thepresent invention updates the TXOP based on the value of the durationfield included in the header. Through this, compatibility with awireless communication terminal that does not support an embodiment ofthe present invention may be achieved.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 20,an access point transmits the RTS-to-Self frame to a plurality ofchannels after waiting for a random value within a contention windowvalue. In a specific embodiment, if a channel is in an idle state for anAIFS, an access point may transmit the RTS-to-Self frame to a pluralityof channels after waiting for a random value within a contention windowvalue. Specifically, the access point transmits an RTS-to-Self frame toa plurality of stations in a BSS through the primary channel Primary CH,the first secondary channel Secondary CH #1, the second secondarychannel Secondary CH #2, the fourth secondary channel Secondary CH #4,the fifth secondary channel Secondary CH #5, the sixth secondary channelSecondary CH #6, and the seventh secondary channel Secondary CH #7, eachof which is in an idle state.

The access point transmits a poll frame to a plurality of stations.Specifically, the access point transmits a poll frame to a plurality ofstations through the primary channel Primary CH.

The plurality of stations receiving the poll frame obtain the channelvector information from the poll frame.

The plurality of stations transmit a CTS frame to the first wirelesscommunication terminal based on the obtained channel vector information.Specifically, each of the first station to the seventh station transmitsa CTS frame through the primary channel Primary CH, the first secondarychannel Secondary CH #1, the second secondary channel Secondary CH #2,the fourth secondary channel Secondary CH #4, the fifth secondarychannel Secondary CH #5, the sixth secondary channel Secondary CH #6,and the seventh secondary channel Secondary CH #7.

The access point transmits plural terminal A-MPDUs to a plurality ofstations that transmit the CTS frame. Specifically, the access pointtransmits plural terminal A-MPDUs to each of the first station to theseventh station through the primary channel Primary CH, the firstsecondary channel Secondary CH #1, the second secondary channelSecondary CH #2, the fourth secondary channel Secondary CH #4, the fifthsecondary channel Secondary CH #5, the sixth secondary channel SecondaryCH #6, and the seventh secondary channel Secondary CH #7. At this time,the access point transmits a header to the first station through theprimary channel Primary CH, transmits a header to the second stationthrough the first secondary channel Secondary CH #1, transmits a headerto the third station through the second secondary channel Secondary CH#2, transmits a header to the fourth station through the fourthsecondary channel Secondary CH #4, transmits a header to the fifthstation through the fifth secondary channel Secondary CH #5, transmits aheader to the sixth station through the sixth secondary channelSecondary CH #1, and transmits a header to the seventh station throughthe seventh secondary channel Secondary CH #7.

The plurality of stations receiving the plural terminal A-MPDUs transmitan ACK frame to the access point. Specifically, the first station to theseventh station transmit an ACK frame through the primary channelPrimary CH, the first secondary channel Secondary CH #1, the secondsecondary channel Secondary CH #2, the fourth secondary channelSecondary CH #4, the fifth secondary channel Secondary CH #5, the sixthsecondary channel Secondary CH #6, and the seventh secondary channelSecondary CH #7.

FIG. 21 is a view illustrating that an access point according to anotherembodiment of the present invention simultaneously transmits data to aplurality of stations using an RTS-to-Self frame.

In the above-described embodiment, the first wireless communicationterminal may transmit the headers of plural terminal A-MPDUs, whichrespectively correspond to the plurality of second wirelesscommunication terminals, to the plurality of second wirelesscommunication terminals through a channel allocated to each secondwireless communication terminal. In another specific embodiment, thesecond wireless communication terminal may transmit a header for aplurality of second wireless communication terminals receiving pluralterminal A-MPDUs through any one channel. At this point, the one channelmay be the primary channel. The header may include the above-describedstart point vector information. As described above, the start pointvector information may include a time and a channel through which thesecond wireless communication terminal receives data. Also, the startpoint vector information may be located after the legacy MPDU header.The header may include all the addresses of the plurality of secondwireless communication terminals receiving the plural terminal A-MPDUs.Therefore, in such an embodiment, it is impossible for a wirelesscommunication terminal that does not support an embodiment of thepresent invention to recognize that a channel is used for thetransmission of plural terminal A-MPDUs through a header.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 21,an access point transmits the RTS-to-Self frame to a plurality ofchannels after waiting for a random value within a contention windowvalue. In a specific embodiment, if a channel is in an idle state for anAIFS, an access point may transmit the RTS-to-Self frame to a pluralityof channels after waiting for a random value within a contention windowvalue. Specifically, the access point transmits an RTS-to-Self frame toa plurality of stations in a BSS through the primary channel Primary CH,the first secondary channel Secondary CH #1, the second secondarychannel Secondary CH #2, the fourth secondary channel Secondary CH #4,the fifth secondary channel Secondary CH #5, the sixth secondary channelSecondary CH #6, and the seventh secondary channel Secondary CH #7, eachof which is in an idle state.

The access point transmits a poll frame to a plurality of stations.Specifically, the access point transmits a poll frame to a plurality ofstations through the primary channel Primary CH.

The plurality of stations receiving the poll frame obtain the channelvector information from the poll frame.

The plurality of stations transmit a CTS frame to the access point basedon the obtained channel vector information. Specifically, each of thefirst station to the seventh station transmits a CTS frame to the accesspoint through the primary channel Primary CH, the first secondarychannel Secondary CH #1, the second secondary channel Secondary CH #2,the fourth secondary channel Secondary CH #4, the fifth secondarychannel Secondary CH #5, the sixth secondary channel Secondary CH #6,and the seventh secondary channel Secondary CH #7.

The access point transmits plural terminal A-MPDUs to a plurality ofstations that transmit the CTS frame. Specifically, the access pointtransmits plural terminal A-MPDUs to each of the first station to theseventh station through the primary channel Primary CH, the firstsecondary channel Secondary CH #1, the second secondary channelSecondary CH #2, the fourth secondary channel Secondary CH #4, the fifthsecondary channel Secondary CH #5, the sixth secondary channel SecondaryCH #6, and the seventh secondary channel Secondary CH #7. At this time,the access point transmits the headers of plural terminal A-MPDUsrespectively corresponding to the plurality of stations through achannel allocated to each of the plurality of stations.

The plurality of stations receiving the plural terminal A-MPDUs transmitan ACK frame to the access point. Specifically, each of the firststation to the seventh station transmits an ACK frame to the accesspoint through the primary channel Primary CH, the first secondarychannel Secondary CH #1, the second secondary channel Secondary CH #2,the fourth secondary channel Secondary CH #4, the fifth secondarychannel Secondary CH #5, the sixth secondary channel Secondary CH #6,and the seventh secondary channel Secondary CH #7.

It is described with reference to FIGS. 22 to 25 that the first wirelesscommunication terminal transmits data instead of plural terminal A-MPDUsto the plurality of second wireless communication terminals. At thistime, the data may be in the form of an A-MPDU.

The first wireless communication terminal may transmit dataasynchronously to the plurality of second wireless communicationterminals. Specifically, the transmission times (i.e., data airtimes) ofdata transmitted from the first wireless communication terminal to theplurality of second wireless communication terminals may be differentfrom each other. Further, the first wireless communication terminal mayreceive data asynchronously from the plurality of second wirelesscommunication terminals. Specifically, the transmission times (i.e.,data airtimes) of data transmitted from each of the plurality of secondwireless communication terminals to the first wireless communicationterminal may be different from each other. The amount of data to betransmitted to each of the plurality of second wireless communicationterminals may be different. Therefore, when the first wirelesscommunication terminal transmits data asynchronously to the plurality ofsecond wireless communication terminals or asynchronously receives datafrom the plurality of second wireless communication terminals, it ispossible to maximize the time that another wireless communicationterminal uses a corresponding channel by reducing the usage time of thecorresponding channel. In addition, the first wireless communicationterminal does not need to perform separate data padding or datafragmentation for synchronization. Also, the first wirelesscommunication terminal does not need to perform scheduling forsynchronization. In such an embodiment, the first wireless communicationterminal may receive an ACK frame from one second wireless communicationterminal while transmitting data to another second wirelesscommunication terminal. It will be described with reference to FIGS. 22and 23 that the first wireless communication terminal transmits data tothe plurality of second wireless communication terminals asynchronously.

FIG. 22 is a view illustrating that an access point according to anembodiment of the present invention allocates one channel to each of aplurality of stations and asynchronously transmits data to the pluralityof stations.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 22,an access point transmits the RTS-to-Self frame to a plurality ofchannels after waiting for a random value within a contention windowvalue. In a specific embodiment, if a channel is in an idle state for anAIFS, an access point may transmit the RTS-to-Self frame to a pluralityof channels after waiting for a random value within a contention windowvalue. Specifically, the access point transmits an RTS-to-Self frame toa plurality of stations in a BSS through the primary channel Primary CH,the first secondary channel Secondary CH #1, the second secondarychannel Secondary CH #2, the fourth secondary channel Secondary CH #4,the fifth secondary channel Secondary CH #5, the sixth secondary channelSecondary CH #6, and the seventh secondary channel Secondary CH #7, eachof which is in an idle state.

The access point transmits a poll frame to a plurality of stations.Specifically, the access point transmits a poll frame to a plurality ofstations through the primary channel Primary CH. The access pointnotifies a station to participate in the transmission to the station ofa corresponding BSS through the transmission of the poll frame.

The plurality of stations receiving the poll frame obtain the channelvector information from the poll frame. Through this, a plurality ofstations participating in the transmission recognize the channelallocated to the plurality of stations themselves.

The plurality of stations transmit a CTS frame to the access point basedon the obtained channel vector information. Specifically, each of thefirst station to the seventh station transmits a CTS frame to the accesspoint through the primary channel Primary CH, the first secondarychannel Secondary CH #1, the second secondary channel Secondary CH #2,the fourth secondary channel Secondary CH #4, the fifth secondarychannel Secondary CH #5, the sixth secondary channel Secondary CH #6,and the seventh secondary channel Secondary CH #7. It is possible tosolve a hidden terminal problem through the transmission of an A-RTSframe of an access point and the transmission of CTS frames of aplurality of stations.

The access point transmits data asynchronously to the plurality ofstations that have transmitted the CTS frame. Specifically, the accesspoint transmits data to each of the first station to the seventh stationat different data transmission times through the primary channel PrimaryCH, the first secondary channel Secondary CH #1, the second secondarychannel Secondary CH #2, the fourth secondary channel Secondary CH #4,the fifth secondary channel Secondary CH #5, the sixth secondary channelSecondary CH #6, and the seventh secondary channel Secondary CH #7.

The plurality of stations receiving the data asynchronously transmitsthe ACK frame to the access point. Specifically, each of the firststation to the seventh station transmits an ACK frame to the accesspoint at the same time through the primary channel Primary CH, the firstsecondary channel Secondary CH #1, the second secondary channelSecondary CH #2, the fourth secondary channel Secondary CH #4, the fifthsecondary channel Secondary CH #5, the sixth secondary channel SecondaryCH #6, and the seventh secondary channel Secondary CH #7.

FIG. 23 is a view illustrating that an access point according to anembodiment of the present invention allocates one or more channels toeach of a plurality of stations and asynchronously transmits data to theplurality of stations.

Although another operation in FIG. 23 is the same as that in FIG. 22,for the sixth station, the access point transmits data through the sixthsecondary channel Secondary CH #6 and the seventh secondary channelSecondary CH #7. At this time, the sixth station recognize that thesixth secondary channel Secondary CH #6 and the seventh secondarychannel Secondary CH #7 are allocated to itself through the poll frame.For such transmission, the sixth station transmits a CTS frame to eachof the sixth secondary channel Secondary CH #6 and the seventh secondarychannel Secondary CH #7. In addition, after receiving the data, thesixth station transmits an ACK frame to each of the sixth secondarychannel Secondary CH #6 and the seventh secondary channel Secondary CH#7.

As described above, when the first wireless communication terminaltransmits data asynchronously to the plurality of second wirelesscommunication terminals and asynchronously receives data from theplurality of second wireless communication terminals, the first wirelesscommunication terminal should transmit data to any one second wirelesscommunication terminal and receive an ACK frame from another secondwireless communication terminal at the same time. Additionally, in sucha case, the operation of allocating, by the first wireless communicationterminal, a channel to the second wireless communication terminal maybecome complicated. In order to solve such a problem, the first wirelesscommunication terminal may transmit data synchronously to the pluralityof second wireless communication terminals. Specifically, thetransmission times (i.e., data airtimes) of data transmitted from thefirst wireless communication terminal to the plurality of secondwireless communication terminals may be the same. In addition, the firstwireless communication terminal may receive data synchronously from theplurality of second wireless communication terminals. Specifically, thetransmission times (i.e., data airtimes) of data transmitted from eachof the plurality of second wireless communication terminals to the firstwireless communication terminal may be the same. For suchsynchronization, the first wireless communication terminal and thesecond wireless communication terminal may perform data padding or datafragmentation. Through this, the operation of allocating, by the firstwireless communication terminal, a channel to the second wirelesscommunication terminal may become simple.

FIG. 24 is a view illustrating that an access point according to anembodiment of the present invention allocates one channel to each of aplurality of stations and synchronously transmits data to the pluralityof stations.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 24,an access point transmits the RTS-to-Self frame to a plurality ofchannels after waiting for a random value within a contention windowvalue. According to a specific embodiment, if a channel is in an idlestate for an AIFS, an access point may transmit the RTS-to-Self frame toa plurality of channels after waiting for a random value within acontention window value. Specifically, the access point transmits anRTS-to-Self frame to a plurality of stations in a BSS through theprimary channel Primary CH, the first secondary channel Secondary CH #1,the second secondary channel Secondary CH #2, the fourth secondarychannel Secondary CH #4, the fifth secondary channel Secondary CH #5,the sixth secondary channel Secondary CH #6, and the seventh secondarychannel Secondary CH #7, each of which is in an idle state.

The access point transmits a poll frame to a plurality of stations.Specifically, the access point transmits a poll frame to a plurality ofstations through the primary channel Primary CH. The access pointnotifies a station to participate in the transmission to the station ofa corresponding BSS through the transmission of the poll frame.

The plurality of stations receiving the poll frame obtain the channelvector information from the poll frame. Through this, a plurality ofstations participating in the transmission recognize the channelallocated to the plurality of stations themselves.

The plurality of stations transmit a CTS frame to the access point basedon the obtained channel vector information. Specifically, each of thefirst station to the seventh station transmits a CTS frame to the accesspoint through the primary channel Primary CH, the first secondarychannel Secondary CH #1, the second secondary channel Secondary CH #2,the fourth secondary channel Secondary CH #4, the fifth secondarychannel Secondary CH #5, the sixth secondary channel Secondary CH #6,and the seventh secondary channel Secondary CH #7. It is possible tosolve a hidden terminal problem through the transmission of an A-RTSframe of an access point and the transmission of CTS frames of aplurality of stations.

The access point transmits data synchronously to the plurality ofstations that transmits the CTS frame. Specifically, the access pointtransmits data to each of the first station to the seventh station atthe same data transmission time through the primary channel Primary CH,the first secondary channel Secondary CH #1, the second secondarychannel Secondary CH #2, the fourth secondary channel Secondary CH #4,the fifth secondary channel Secondary CH #5, the sixth secondary channelSecondary CH #6, and the seventh secondary channel Secondary CH #7.

The plurality of stations receiving the data synchronously transmits theACK frame to the access point. Specifically, each of the first stationto the seventh station transmits an ACK frame to the access point at thesame time through the primary channel Primary CH, the first secondarychannel Secondary CH #1, the second secondary channel Secondary CH #2,the fourth secondary channel Secondary CH #4, the fifth secondarychannel Secondary CH #5, the sixth secondary channel Secondary CH #6,and the seventh secondary channel Secondary CH #7.

FIG. 25 is a view illustrating that an access point according to anembodiment of the present invention allocates one or more channels toeach of a plurality of stations and synchronously transmits data to theplurality of stations.

Although another operation in FIG. 25 is the same as that in FIG. 24,for the sixth station, the access point transmits data through the sixthsecondary channel Secondary CH #6) and the seventh secondary channelSecondary CH #7. At this time, the sixth station recognizes that thesixth secondary channel Secondary CH #6 and the seventh secondarychannel Secondary CH #7 are allocated to the sixth station through thepoll frame. For such transmission, the sixth station transmits a CTSframe to each of the sixth secondary channel Secondary CH #6 and theseventh secondary channel Secondary CH #7. In addition, after receivingthe data, the sixth station transmits an ACK frame to each of the sixthsecondary channel Secondary CH #6 and the seventh secondary channelSecondary CH #7.

Through such an embodiment, the operation of the first wirelesscommunication terminal to allocate a channel to the second wirelesscommunication terminal may become simple. In addition, the firstwireless communication terminal does not need to receive an ACK framefrom one second wireless communication terminal while transmitting datato another second wireless communication terminal.

FIG. 26 is a view illustrating that an access point according to anembodiment of the present invention transmits data to a plurality ofstations when not receiving a CTS frame from any one station.

The first wireless communication terminal transmits data to the secondwireless communication terminal that transmits the CTS frame. If eventhe second wireless communication terminal that receives a channel froma poll frame does not transmit a CTS frame, the first wirelesscommunication terminal does not transmit data to a correspondingterminal. This may be applied to all of the data transmissionembodiments using the above-described poll frame.

The embodiment of FIG. 26 shows that an access point according to anembodiment of the present invention transmits data to a plurality ofstations when one station does not transmit a CTS frame by a hiddennode.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 26,an access point transmits the RTS-to-Self frame to a plurality ofchannels after waiting for a random value within a contention windowvalue. According to a specific embodiment, if a channel is in an idlestate for an AIFS, an access point may transmit the RTS-to-Self frame toa plurality of channels after waiting for a random value within acontention window value. Specifically, the access point transmits anRTS-to-Self frame to a plurality of stations in a BSS through theprimary channel Primary CH, the first secondary channel Secondary CH #1,the second secondary channel Secondary CH #2, the third secondarychannel Secondary CH #3, the fourth secondary channel Secondary CH #4,the fifth secondary channel Secondary CH #5, the sixth secondary channelSecondary CH #6, and the seventh secondary channel Secondary CH #7, eachof which is in an idle state.

The access point transmits a poll frame to a plurality of stations.Specifically, the access point transmits a poll frame to a plurality ofstations through the primary channel Primary CH. At this time, theaccess point allocates the primary channel Primary CH and the firstsecondary channel Secondary CH #1 to the seventh secondary channelSecondary CH #7 to the first station to the eighth station,respectively. The access point notifies a channel allocated to aplurality of stations to the station of a corresponding BSS through thetransmission of the poll frame.

The plurality of stations receiving the poll frame obtain the channelvector information from the poll frame. Through this, a plurality ofstations participating in the transmission recognize the channelallocated to the plurality of stations themselves.

The plurality of stations receiving the poll frame transmit a CTS frameto each of the plurality of stations through the allocated channel.Specifically, the fourth station whose allocated channel is not in anidle state does not transmit a CTS frame, and the first station to thirdstation and the fifth station to the eighth station respectivelytransmit CTS frames to the access point through the primary channelPrimary CH, the first secondary channel Secondary CH #1 and the secondsecondary channel Secondary CH #2, and the fourth secondary channelSecondary CH #4 to the seventh secondary channel Secondary CH #7.

The access point transmits data to the station that transmits the CTSframe. At this time, the access point may transmit data according tovarious embodiments described above.

In the above-described embodiment, the first wireless communicationterminal may receive data from the plurality of second wirelesscommunication terminals at the same time. However, when the firstwireless communication terminal is not able to simultaneously receivedata from the plurality of second wireless communication terminals, asin the above-described embodiments, the plurality of second wirelesscommunication terminals may not simultaneously transmit CTS frames tothe first wireless communication terminal. Therefore, in such a case,another method is required for the plurality of second wirelesscommunication terminals to transmit CTS frames to the first wirelesscommunication terminals.

FIG. 27 is a view illustrating an operation of an access point tosimultaneously transmit data to a plurality of stations when the accesspoint is not able to simultaneously receive data from the plurality ofstations according to another embodiment of the present invention.

The plurality of second wireless communication terminals maysequentially transmit CTS frames to the first wireless communicationterminal. At this time, the plurality of second wireless communicationterminals may sequentially transmit CTS frames to the first wirelesscommunication terminal at a predetermined time interval. Specifically,the second wireless communication terminal may wait for a timecorresponding to an integer multiple of the sum of the transmissiontimes of an SIFS and a CTS frame, and then transmit the CTS frame to thefirst wireless communication terminal. In addition, the plurality ofsecond wireless communication terminals may sequentially transmit CTSframes to the first wireless communication terminal based on the pollframe. In a specific embodiment, the second wireless communicationterminal may obtain the CTS frame transmission order specified to thesecond wireless communication terminal from the poll frame.Specifically, the arrangement order of the address of the secondwireless communication terminal included in the poll frame may indicatethe CTS frame transmission order of the corresponding second wirelesscommunication terminal. At this time, a channel included with theaddress of the second wireless communication terminal of the poll framemay indicate a channel allocated to the second wireless communicationterminal as described above.

In another specific embodiment, the number of second wirelesscommunication terminals for simultaneously transmitting data to thefirst wireless communication terminal may be limited. In this case,after a predetermined number of the second wireless communicationterminals among the plurality of second wireless communication terminalstransmit CTS frames to the first wireless communication terminal, theremaining second wireless communication terminal may transmit the CTSframes to the first wireless communication terminal. At this time, thesecond wireless communication terminal may obtain from the poll framethe order in which the second wireless communication terminal transmitsCTS frames to the first wireless communication terminal. Specifically,the arrangement order of the address of the second wirelesscommunication terminal included in the CTS frame may indicate the orderin which the corresponding second wireless communication terminaltransmits the CTS frame.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 27,an access point transmits the RTS-to-Self frame to a plurality ofchannels after waiting for a random value within a contention windowvalue. According to a specific embodiment, if a channel is in an idlestate for an AIFS, an access point may transmit the RTS-to-Self frame toa plurality of channels after waiting for a random value within acontention window value. Specifically, the access point transmits anRTS-to-Self frame to a plurality of stations in a BSS through theprimary channel Primary CH, the first secondary channel Secondary CH #1,the second secondary channel Secondary CH #2, the fourth secondarychannel Secondary CH #4, the fifth secondary channel Secondary CH #5,the sixth secondary channel Secondary CH #6, and the seventh secondarychannel Secondary CH #7, each of which is in an idle state.

The access point transmits a poll frame to a plurality of stations.Specifically, the access point transmits a poll frame to a plurality ofstations through the primary channel Primary CH. The access pointnotifies a channel allocated to a plurality of stations to the stationof a corresponding BSS through the transmission of the poll frame.

The plurality of stations receiving the poll frame obtain the channelvector information from the poll frame. Through this, a plurality ofstations participating in the transmission recognize the channelallocated to the plurality of stations themselves.

The plurality of stations sequentially transmit the CTS frame to theaccess point through the channel allocated to the plurality of stationsthe plurality of stations. Specifically, after receiving the poll frameand an SIFS elapses, the first station transmits the CTS frame to theaccess point through the primary channel Primary CH. After the firststation transmits the CTS frame and an SIFS elapses, the second stationtransmits a CTS frame to the access point through the first secondarychannel Secondary CH #1. After the second station transmits the CTSframe and an SIFS elapses, the third station transmits a CTS frame tothe access point through the second secondary channel Secondary CH #2.After the third station transmits the CTS frame and an SIFS elapses, thefifth station transmits a CTS frame to the access point through thefourth secondary channel Secondary CH #4. After the fifth stationtransmits the CTS frame and an SIFS elapses, the sixth station transmitsa CTS frame to the access point through the fifth secondary channelSecondary CH #5. After the sixth station transmits the CTS frame and anSIFS elapses, the seventh station transmits a CTS frame to the accesspoint through the sixth secondary channel Secondary CH #6. After theseventh station transmits the CTS frame and an SIFS elapses, the eighthstation transmits a CTS frame to the access point through the seventhsecondary channel Secondary CH #7. At this time, each of the pluralityof stations may obtain a CTS frame transmission order specified to theplurality of stations the plurality of stations based on the poll frameas described above. Specifically, the arrangement order of the addressof a station included in the poll frame may indicate the CTS frametransmission order of the corresponding station.

The access point transmits data to the station that transmits the CTSframe. At this time, the access point may transmit data according tovarious embodiments described above.

In the above described embodiment, the second wireless communicationterminal transmits the CTS frame to the first wireless communicationterminal when a predetermined time elapses from the time when the firstwireless communication terminal transmits the poll frame to the secondwireless communication terminal. In a specific embodiment, thepredetermined time may be an SIFS. If the second wireless communicationterminal takes a long time to process the poll frame, the predeterminedtime may be longer than the SIFS. Specifically, the predetermined timemay be a PCF inter-frame space (PIFS) defined in 802.11. For example,after a PIFS from the time when the first wireless communicationterminal transmits the poll frame to the plurality of second wirelesscommunication terminals, the plurality of second wireless communicationterminals may transmit a CTS frame to the first wireless communicationterminal.

FIG. 28 is a view illustrating that when an access point according to anembodiment of the present invention transmits data to a plurality ofstations, after a PIFS from the time when the access point transmits apoll frame to the plurality of stations, the plurality of stationstransmit a CTS frame to the access point.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 28,an access point transmits the RTS-to-Self frame to a plurality ofchannels after waiting for a random value within a contention windowvalue. According to a specific embodiment, if a channel is in an idlestate for an AIFS, an access point may transmit the RTS-to-Self frame toa plurality of channels after waiting for a random value within acontention window value. Specifically, the access point transmits anRTS-to-Self frame to a plurality of stations in a BSS through theprimary channel Primary CH, the first secondary channel Secondary CH #1,the second secondary channel Secondary CH #2, the fourth secondarychannel Secondary CH #4, the fifth secondary channel Secondary CH #5,the sixth secondary channel Secondary CH #6, and the seventh secondarychannel Secondary CH #7, each of which is in an idle state.

The access point transmits a poll frame to a plurality of stations.Specifically, the access point transmits a poll frame to a plurality ofstations through the primary channel Primary CH. The access pointnotifies a channel allocated to a plurality of stations to the stationof a corresponding BSS through the transmission of the poll frame.

The plurality of stations receiving the poll frame obtain the channelvector information from the poll frame. Through this, a plurality ofstations participating in the transmission recognize the channelallocated to the plurality of stations themselves.

After a PIFS from the time when the access point transmits the pollframe, the plurality of stations transmit a CTS frame through thechannel allocated to the plurality of stations themselves. The fourthstation whose allocated channel is not in an idle state does nottransmit a CTS frame. Each of the first station to the third station andthe fifth station to the eighth station transmits a CTS frame to theaccess point through the primary channel Primary CH, the first secondarychannel Secondary CH #1 and the second secondary channel Secondary CH#2, and the fourth secondary channel Secondary CH #4 to the seventhsecondary channel Secondary CH #7.

The access point transmits data to the station that transmits the CTSframe. At this time, the access point may transmit data according tovarious embodiments described above.

In the above-described embodiment, the first wireless communicationterminal transmits the RTS-to-Self frame to the second wirelesscommunication terminal, and then transmits the poll frame. According toa specific embodiment, the first wireless communication terminal maytransmit the poll frame and then transmit the RTS-to-Self frame. In sucha case, the second wireless communication terminal may recognize thatdata is transmitted to the second wireless communication terminal beforereceiving the RTS-to-Self frame. In addition, at this time, the secondwireless communication terminal may recognize the channel allocated tothe second wireless communication terminal. Accordingly, the secondwireless communication terminal has a sufficient time to prepare for CTSframe transmission to the first wireless communication terminal.

FIG. 29 is a view illustrating that an access point according to anembodiment of the present invention transmits a poll frame to aplurality of stations and transmits data after transmitting anRTS-to-Self frame.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 29,an access point transmits a poll frame to a plurality of stations afterwaiting for a random value within a contention window value. In aspecific embodiment, if a channel is in an idle state for an AIFS, anaccess point may transmit the poll frame to a plurality of stationsafter waiting for a random value within a contention window value.Specifically, the access point transmits a poll frame to a plurality ofstations through the primary channel Primary CH. The access pointnotifies a channel allocated to a plurality of stations to the stationof a corresponding BSS through the transmission of the poll frame. Inaddition, the plurality of stations receiving the poll frame obtain thechannel vector information from the poll frame. Through this, aplurality of stations participating in the transmission recognize thechannel allocated to the plurality of stations themselves. Through this,before receiving the RTS-to-Self frame, the plurality of stations mayknow the data to be transmitted to them and the channel allocated tothem. Through this, the plurality of stations may prepare for thetransmission of a CTS frame in advance.

The access point transmits the RTS-to-Self frame through a plurality ofchannels. Specifically, the access point transmits an RTS-to-Self frameto a plurality of stations in a BSS through the primary channel PrimaryCH, the first secondary channel Secondary CH #1, the second secondarychannel Secondary CH #2, the fourth secondary channel Secondary CH #4,the fifth secondary channel Secondary CH #5, the sixth secondary channelSecondary CH #6, and the seventh secondary channel Secondary CH #7, eachof which is in an idle state.

The plurality of stations transmit the CTS frame through the channelallocated to the plurality of stations the plurality of stations. Thefourth station whose allocated channel is not in an idle state does nottransmit a CTS frame. Each of the first station to the third station andthe fifth station to the eighth station transmits a CTS frame to theaccess point through the primary channel Primary CH, the first secondarychannel Secondary CH #1 and the second secondary channel Secondary CH#2, and the fourth secondary channel Secondary CH #4 to the seventhsecondary channel Secondary CH #7.

The access point transmits data to the station that transmits the CTSframe. At this time, the access point may transmit data according tovarious embodiments described above.

In another specific embodiment, the first wireless communicationterminal may transmit data to the plurality of wireless communicationterminals by modifying the RTS frame without using the poll frame. Forconvenience of description, the modified RTS frame is referred to as anM-RTS frame. This will be described with reference to FIG. 30.

FIG. 30 is a view illustrating that an access point according to anembodiment of the present invention transmits data to a plurality ofstations using an M-RTS frame.

The first wireless communication terminal may transmit a plurality ofM-RTS frames to the plurality of second wireless communicationterminals, respectively. At this time, the M-RTS frame may be a legacyRTS frame in which the address of the second wireless communicationterminal allocated with the channel through which the M-RTS frame istransmitted is set to the RA field value. Therefore, in the plurality ofM-RTS frames, the values of the RA fields are different. In such anembodiment, the second wireless communication terminal should scan allchannels.

In another specific embodiment, the first wireless communicationterminal may transmit an M-RTS frame to the plurality of second wirelesscommunication terminals through any one channel. At this point, the onechannel may be the primary channel. Also, the M-RTS frame may have astructure in which the legacy RTS frame further includes the channelvector information described above. For example, the structure of theM-RTS frame may be a structure in which the channel vector informationis located after the FCS field of the legacy RTS frame.

If a channel is in an idle state for a DIFS in an embodiment of FIG. 30,an access point transmits the M-RTS frame to a plurality of stationsthrough a plurality of channels after waiting for a random value withina contention window value. In a specific embodiment, if a channel is inan idle state for an AIFS, an access point may transmit the M-RTS frameto a plurality of stations through a plurality of channels after waitingfor a random value within a contention window value. Specifically, theaccess point transmits an M-RTS frame to a plurality of stations throughthe primary channel Primary CH, the first secondary channel Secondary CH#1, the second secondary channel Secondary CH #2, the fourth secondarychannel Secondary CH #4, the fifth secondary channel Secondary CH #5,the sixth secondary channel Secondary CH #6, and the seventh secondarychannel Secondary CH #7, each of which is in an idle state.

The plurality of stations recognize a channel allocated to the pluralityof stations the plurality of stations based on the channel through whichthe M-RTS is transmitted and the RA field value of the M-RTS.

The plurality of stations transmit the CTS frame through the channelallocated to the plurality of stations the plurality of stations. Thefourth station whose allocated channel is not in an idle state does nottransmit a CTS frame. Each of the first station to the third station andthe fifth station to the eighth station transmits a CTS frame to theaccess point through the primary channel Primary CH, the first secondarychannel Secondary CH #1 and the second secondary channel Secondary CH#2, and the fourth secondary channel Secondary CH #4 to the seventhsecondary channel Secondary CH #7.

The access point transmits data to the station that transmits the CTSframe. At this time, the access point may transmit data according tovarious embodiments described above.

The plurality of second wireless communication terminals maysimultaneously transmit data to the first wireless communicationterminal as described above. For this, a method of the first wirelesscommunication terminal to allocate a channel to the plurality of secondwireless communication terminals and a method of the plurality of secondwireless communication terminals to reserve a TXOP are required. Thiswill be described with reference to FIGS. 31 to 41. In particular, it isdescribed with reference to FIGS. 31 to 37 that after the first wirelesscommunication terminal transmits data to a plurality of second wirelesscommunication terminals, a plurality of second wireless communicationterminals transmit data to the first wireless terminal. For convenienceof description, what the first wireless communication terminal transmitsdata to a plurality of second wireless communication terminals isreferred to as downlink transmission, and what a plurality of secondwireless communication terminals transmit data to the first wirelessterminal is referred to as an uplink transmission.

The second wireless communication terminal may notify whether or notthere is data to be transmitted to the first wireless communicationterminal by transmitting a specific frame. Accordingly, the frametransmitted from the second wireless communication terminal to the firstwireless communication terminal may indicate whether there is data to betransmitted from the second wireless communication terminal to the firstwireless communication terminal. In a specific embodiment, an ACK frametransmitted from the second wireless communication terminal to the firstwireless communication terminal may indicate whether there is data to betransmitted from the second wireless communication terminal to the firstwireless communication terminal. In addition, the more data field of aframe transmitted from the second wireless communication terminal to thefirst wireless communication terminal may indicate whether there is datato be transmitted from the second wireless communication terminal to thefirst wireless communication terminal. For example, the more data fieldof an ACK frame transmitted from the second wireless communicationterminal to the first wireless communication terminal may indicatewhether there is data to be transmitted from the second wirelesscommunication terminal to the first wireless communication terminal. Themore data field indicates that there is a bufferable unit (BU) to betransmitted from an access point to a station in a power saving (PS)mode. Therefore, a station receiving a frame in which the more datafield is 1 continuously wakes up in the PS mode and waits for the datatransmission of an access point. However, if the access point is not ina downlink transmission session for transmitting data to the station,the more data field is not used. Accordingly, as described above, thesecond wireless communication terminal may use the more data field tonotify whether there is data to be transmitted to the first wirelesscommunication terminal. Through such an embodiment, the first wirelesscommunication terminal may know that there is data to be transmittedfrom the second wireless communication terminal to the first wirelesscommunication terminal itself. Specifically, the presence of data to betransmitted may mean a buffer status indicating whether there is data tobe transmitted to the first wireless communication terminal in thebuffer of the second wireless communication terminal.

The first wireless communication terminal allocates a channel to be usedby the second wireless communication terminal. The first wirelesscommunication terminal transmits the above-described poll frame to theplurality of second wireless communication terminals. At this time, thepoll frame may include channel vector information indicating informationof a channel allocated to the second wireless communication terminal.Additionally, the first wireless communication terminal may transmit thepoll frame through a primary channel. In another specific embodiment,the first wireless communication terminal may transmit the poll frame tothe plurality of second wireless communication terminals through thechannel used for transmitting data. In another specific embodiment, thefirst wireless communication terminal may transmit the poll frame to theplurality of second wireless communication terminals through a channelallocated to each second wireless communication terminal. In addition,the poll frame may be referred to as a trigger frame as described above.

The second wireless communication terminal obtains channel vectorinformation based on the poll frame. Specifically, the second wirelesscommunication terminal may obtain information on the channel that thefirst wireless communication terminal allocates to the second wirelesscommunication terminal the second wireless communication terminal fromthe channel vector information of the poll frame.

The second wireless communication terminal transmits data to the firstwireless communication terminal through the channel allocated to thesecond wireless communication terminal the second wireless communicationterminal. According to a specific embodiment, the second wirelesscommunication terminal may transmit data to the first wirelesscommunication terminal without receiving a separate frame afterreceiving the poll frame. Specifically, if all the TXOPs of the channelsused in the uplink transmission session are protected in the downlinktransmission session, the second wireless communication terminal maytransmit data to the first wireless communication terminal afterreceiving the poll frame. At this time, since the second wirelesscommunication terminal receives the poll frame and transmits data aftera predetermined time, the data transmission time becomes identical tothat of another second wireless communication terminal. In anotherspecific embodiment, the second wireless communication terminal maytransmit the ACK frame for the poll frame to terminate the downlinktransmission session and transmit data to the first wirelesscommunication terminal. Specifically, after the second wirelesscommunication terminal transmits the ACK frame, the first wirelesscommunication terminal transmits the CTS-to-Self frame to reserve theTXOP of the uplink transmission session. At this time, the CTS-to-Selfframe indicates a case in which the RA field of the CTS frame is the MACaddress of a wireless communication terminal transmitting the CTS frame.The wireless communication terminal receiving the CTS-to-Self frame maynot access the corresponding channel. Therefore, the CTS-to-Self frameserves to reserve the TXOP. After the first wireless communicationterminal obtains the TXOP of the uplink transmission session, the secondwireless communication terminal may transmit data to the first wirelesscommunication terminal.

FIG. 31 is a view illustrating that a plurality of stations according toan embodiment of the present invention transmit data to an access pointafter receiving data from the access point.

In the embodiment of FIG. 31, the access point transmits data to theplurality of stations. Specifically, the access point transmits data tothe first station, the third station, and the fourth station. For this,the access point transmits an RTS frame to the plurality of stations,and receives a CTS frame from the plurality of stations to reserve aTXOP.

The first station, the third station, and the fourth station, whichreceive data from the access point, transmit an ACK frame to the accesspoint. At this time, the first station and the third station, which havedata to be transmitted to the access point, transmit an ACK frameindicating whether there is data to be transmitted. At this time, if thevalue of the more data field in the ACK frame is 1, the ACK frame mayindicate that the station transmitting the ACK frame has data to betransmitted to the access point.

The access point allocates a channel to the first station and the thirdstation. The access point transmits a poll frame including informationon the allocated channel to the first station and the third station.

The first station and the third station receive the poll frame andtransmit an ACK frame for the poll frame to the access point. Asdescribed above, after receiving the poll frame, the first station andthe third station may transmit data to the access point withouttransmitting a separate frame.

The access point transmits the RTS-to-Self frame to a plurality ofstations. Through this, the access point obtains a TXOP through whichthe first station and the third station are able to transmit data to thefirst station and the third station themselves.

Each of the first station and the third station transmits data to theaccess point through a channel allocated to the first station and thethird station themselves.

The first wireless communication terminal may allocate a channel to beused for the uplink transmission session to the plurality of secondwireless communication terminals based on the channel used in thedownlink transmission session and the plurality of second wirelesscommunication terminals participating in the downlink transmission. Thiswill be described with reference to FIG. 32.

FIG. 32 is a view illustrating that each of a plurality of stationsaccording to an embodiment of the present invention transmits data to anaccess point through a channel used when the access point transmits datato each of the plurality of stations.

The first wireless communication terminal may allocate a channel usedfor downlink transmission to the second wireless communication terminalparticipating in downlink transmission as a channel for uplinktransmission. At this time, each of the first wireless communicationterminal and the second wireless communication terminal may performdownlink transmission using the TXOP obtained during the downlinktransmission. Specifically, the first wireless communication terminaland the second wireless communication terminal may use the TXOP set andupdated through the duration field values of the RTS frame and the CTSframe. Such a channel allocation may be specifically performed throughthe following operations.

The second wireless communication terminal may transmit to the firstwireless communication terminal at least any one of informationindicating whether there is data to be transmitted to the first wirelesscommunication terminal, information on the size of data to betransmitted to the first wireless communication terminal, andinformation on an available channel. Specifically, the second wirelesscommunication terminal may transmit to the first wireless communicationterminal a frame including at least any one of information indicatingwhether there is data to be transmitted to the first wirelesscommunication terminal, information on the size of data to betransmitted to the first wireless communication terminal, andinformation on an available channel. For example, the ACK frametransmitted from the second wireless communication terminal to the firstwireless communication terminal includes at least one of informationindicating whether there is data to be transmitted to the first wirelesscommunication terminal, the size of data to be transmitted to the firstwireless communication terminal, and information on an availablechannel. At this time, the available channel information notifies thefirst wireless communication terminal of a hidden terminal that thefirst wireless communication terminal does not detect. Through this, thefirst wireless communication terminal may allocate a channel except fora channel used by the hidden terminal, so that it prevents transmissioncollision with the hidden terminal during the data transmission from thesecond wireless communication terminal to the first wirelesscommunication terminal. Further, the first wireless communicationterminal may prepare a buffer for data reception based on the size ofdata to be transmitted.

The first wireless communication terminal allocates a channel to each ofthe plurality of second wireless communication terminals based oninformation received from the second wireless communication terminal, achannel used for the downlink transmission, and the plurality of secondwireless communication terminals participating in the downlinktransmission. Specifically, the first wireless communication terminalmay allocate a channel allocated during downlink transmission to theplurality of wireless second wireless communication terminals as anuplink transmission channel. Through this, the first wirelesscommunication terminal and the second wireless communication terminalmay utilize the TXOP obtained during a downlink transmission session.

The first wireless communication terminal transmits a poll frame to aplurality of stations. As described above, the poll frame includesinformation on a channel allocated to the second wireless communicationterminal by the first wireless communication terminal. The firstwireless communication terminal may transmit a poll frame to theplurality of stations after a predetermined time from the time when theACK frame is received. Specifically, the first wireless communicationterminal may transmit a poll frame to the plurality of stations after anSIFS from the time when the ACK frame is received. According to thecomplexity of scheduling or a calculation time, the first wirelesscommunication terminal may transmit a poll frame to the plurality ofstations after more than an SIFS from the time when the ACK frame isreceived.

In the embodiment of FIG. 32, the access point transmits data to theplurality of stations. Specifically, the access point transmits data toeach of the first station to the third station and the fifth station tothe seventh station through the primary channel Primary CH, the firstsecondary channel Secondary CH #1 and the second secondary channelSecondary CH #2, and the fourth secondary channel Secondary CH #4 to theseventh secondary channel Secondary CH #7. For this, the access pointtransmits an RTS frame to the plurality of stations, and receives a CTSframe from the plurality of stations to reserve a TXOP.

The plurality of stations receiving data from the access point transmitan ACK frame to the access point through a channel allocated to each ofthe plurality of stations. Specifically, each of the first station tothe third station and the fifth station to the eighth station transmitsan ACK frame to the access point through the primary channel Primary CH,the first secondary channel Secondary CH #1 and the second secondarychannel Secondary CH #2, and the fourth secondary channel Secondary CH#4 to the seventh secondary channel Secondary CH #7. At this time, eachof the first station to the third stations and the sixth station and theseventh station, which have data to be transmitted to the access point,transmits an ACK frame indicating whether there is data to betransmitted. At this time, if the value of the more data field in theACK frame is 1, the ACK frame may indicate that the station transmittingthe ACK frame has data to be transmitted to the access point.

The access point allocates a channel to be used for data transmission tothe plurality of stations that transmit an ACK frame indicating thatthere is data to be transmitted to the access point. Specifically, theaccess point allocates a channel to be used for data transmission toeach of the first station to the third station and the sixth station andthe seventh station. Specifically, the access point may allocatechannels, which are used by each of the first station to the thirdstation and the sixth station and the seventh station in a downlinktransmission session, to the first station to the third station and thesixth station, respectively.

The access point transmits a poll frame including information on theallocated channel to a plurality of stations. The access point transmitsthe poll frame including the information on the allocated channel to thefirst station to the third station and the sixth station and the seventhstation.

After receiving the poll frame, the plurality of stations transmit datato the access point. Specifically, the first station to the thirdstation and the sixth station and the seventh station receive the pollframe, and then transmit data to the access point.

Each of the plurality of stations transmits data to the access pointthrough a channel allocated to the plurality of stations themselves.Each of the first station to the third station and the sixth station andthe seventh station transmits data to the access point through theprimary channel Primary CH, the first secondary channel Secondary CH #1and the second secondary channel Secondary CH #2, and the fifthsecondary channel Secondary CH #5 to the seventh secondary channelSecondary CH #7.

The access point receiving the data transmits an ACK frame to the firststation to the third station and the sixth station and the seventhstation through the primary channel Primary CH, the first secondarychannel Secondary CH #1 and the second secondary channel Secondary CH#2, and the fifth secondary channel Secondary CH #5 to the seventhsecondary channel Secondary CH #7.

However, only some of the plurality of second wireless communicationterminals that receive data from the first wireless communicationterminal may transmit data to the first wireless communication terminal.Alternatively, there may be a large difference between the size of thedata received from the first wireless communication terminal and thesize of the data to be transmitted by the second wireless communicationterminal. In such a case, as described with reference to FIG. 32, it isinefficient in terms of bandwidth utilization that the second wirelesscommunication terminal uses a channel used for downlink transmission asit is. Therefore, the first wireless communication terminal may allocatea channel to the second wireless communication terminal withoutconsidering a channel allocated to the second wireless communicationterminal in downlink transmission. This will be described with referenceto FIGS. 33 and 34.

FIG. 33 is a view illustrating that a plurality of stations according toan embodiment of the present invention receive an allocated channel totransmit data to an access point regardless of whether the access pointuses a corresponding channel when transmitting data to the plurality ofstations.

The first wireless communication terminal may allocate a channel foruplink transmission to each of the plurality of second wirelesscommunication terminals regardless of whether a corresponding channel isused in downlink transmission to the plurality of second wirelesscommunication terminals. In such a case, a channel may be allocated tomatch the current channel situation, and the channel usage rate may beincreased. Therefore, the data transmission speed from the secondwireless communication terminal to the first wireless communicationterminal may be improved.

As described above, the second wireless communication terminal maytransmit to the first wireless communication terminal at least any oneof information indicating whether there is data to be transmitted to thefirst wireless communication terminal, information on the size of datato be transmitted to the first wireless communication terminal, andinformation on an available channel. Specifically, the second wirelesscommunication terminal may transmit to the first wireless communicationterminal a frame including at least any one of information indicatingwhether there is data to be transmitted to the first wirelesscommunication terminal, information on the size of data to betransmitted to the first wireless communication terminal, andinformation on an available channel. For example, the ACK frametransmitted from the second wireless communication terminal to the firstwireless communication terminal includes at least one of informationindicating whether there is data to be transmitted to the first wirelesscommunication terminal, the size of data to be transmitted to the firstwireless communication terminal, and information on an availablechannel. At this time, the available channel information notifies thefirst wireless communication terminal of a hidden terminal that thefirst wireless communication terminal does not detect. Through this, thefirst wireless communication terminal may allocate a channel except fora channel used by the hidden terminal, so that it prevents transmissioncollision with the hidden terminal during the data transmission from thesecond wireless communication terminal to the first wirelesscommunication terminal. Further, the first wireless communicationterminal may prepare a buffer for data reception based on the size ofdata to be transmitted.

The first wireless communication terminal may allocate a channel to eachof the plurality of second wireless communication terminals based on theinformation received from the second wireless communication terminal.Specifically, the first wireless communication terminal may allocate achannel to be used for uplink transmission by the second wirelesscommunication terminal based on at least any one of informationindicating whether there is data to be transmitted by the secondwireless communication terminal, information on the size of data to betransmitted by the second wireless communication terminal, andinformation on an available channel. For example, the first wirelesscommunication terminal may allocate a channel bandwidth according to thesize of data to be transmitted by each of the plurality of secondwireless communication terminals. Through this, the first wirelesscommunication terminal may maximize the channel usage efficiency.

However, unlike the embodiment of FIG. 32, since the TXOP obtainedduring uplink transmission is not utilized, there may be a risk that acollision with the transmission of another wireless communicationterminal occurs when the second wireless communication terminaltransmits data to the first wireless communication terminal.Specifically, when the first wireless communication terminal transmitsan RTS frame through all the channels in an idle state before downlinktransmission, a wireless communication terminal around the firstwireless communication terminal may set an NAV value by the RTS frame.Therefore, the probability of collision with the data transmission ofthe wireless communication terminal around the first wirelesscommunication terminal is low. However, since the second wirelesscommunication terminal does not transmit a CTS frame previously throughan allocated channel, the NAV may not be set. However, even in such acase, since the wireless communication terminal around the secondwireless communication terminal performs a Clear Channel Assessment(CCA) by Energy Detection (ED), the possibility of data transmissioncollision may not be high.

In the embodiment of FIG. 33, the access point transmits data to theplurality of stations. Specifically, the access point transmits data toeach of the first station to the third station and the fifth station tothe seventh station through the primary channel Primary CH, the firstsecondary channel Secondary CH #1 and the second secondary channelSecondary CH #2, and the fourth secondary channel Secondary CH #4 to theseventh secondary channel Secondary CH #7. For this, the access pointtransmits an RTS frame to the plurality of stations, and receives a CTSframe from the plurality of stations to reserve a TXOP.

The plurality of stations receiving data from the access point transmitan ACK frame to the access point through a channel allocated to each ofthe plurality of stations. Specifically, each of the first station tothe third station and the fifth station to the eighth station transmitsan ACK frame to the access point through the primary channel Primary CH,the first secondary channel Secondary CH #1 and the second secondarychannel Secondary CH #2, and the fourth secondary channel Secondary CH#4 to the seventh secondary channel Secondary CH #7. At this time, eachof the first station to the third stations and the sixth station and theseventh station, which have data to be transmitted to the access point,transmits an ACK frame indicating that there is data to be transmitted.At this time, if the value of the more data field in the ACK frame is 1,the ACK frame may indicate that the station transmitting the ACK framehas data to be transmitted to the access point.

The access point allocates a channel to be used for data transmission tothe plurality of stations that transmit an ACK frame indicating thatthere is data to be transmitted to the access point. Specifically, theaccess point allocates a channel to be used for data transmission toeach of the first station to the third station and the sixth station andthe seventh station. Specifically, the access point may allocate achannel to be used for uplink transmission to each of the first stationto the third station and the sixth station regardless of whether thecorresponding channel is used in the downlink transmission session.Specifically, the access point allocates the primary channel Primary CHto the first station, allocates the first secondary channel Secondary CH#1 to the second station, allocates the second secondary channelSecondary CH #2 to the third station, allocates the fourth secondarychannel Secondary CH #4 and the fifth secondary channel Secondary CH #5to the sixth station, and allocates the sixth secondary channelSecondary CH #6 and the seventh secondary channel Secondary CH #7 to theseventh station. At this time, the access point allocates the fourthsecondary channel Secondary CH #4 not being used by the sixth station tothe sixth station.

The access point transmits a poll frame including information on theallocated channel to the plurality of stations. The access pointtransmits the poll frame including the information on the allocatedchannel to the first station to the third station and the sixth stationand the seventh station.

After receiving the poll frame, the plurality of stations transmit datato the access point. Specifically, the first station to the thirdstation and the sixth station and the seventh station receive the pollframe, and then transmit data to the access point.

Each of the plurality of stations transmits data to the access pointthrough a channel allocated to the plurality of stations themselves.Each of the first station to the third station and the sixth station andthe seventh station transmits data to the access point through theprimary channel Primary CH, the first secondary channel Secondary CH #1and the second secondary channel Secondary CH #2, and the fifthsecondary channel Secondary CH #5 to the seventh secondary channelSecondary CH #7.

The access point receiving the data transmits an ACK frame to the firststation to the third station and the sixth station and the seventhstation through the primary channel Primary CH, the first secondarychannel Secondary CH #1 and the second secondary channel Secondary CH#2, and the fifth secondary channel Secondary CH #5 to the seventhsecondary channel Secondary CH #7.

As the embodiments of FIGS. 31 and 32 are described above, it isdescribed that the second wireless communication terminal transmitsinformation on available channels to the first wireless communicationterminal, and through this, collision with the transmission of anotherwireless communication terminal is prevented during data transmission.The first wireless communication terminal may allocate a channel to beused during the uplink transmission of the second wireless communicationterminal based on available channel information transmitted by thesecond wireless communication terminal and available channel informationdetected by the first wireless communication terminal. This will bedescribed with reference to FIG. 34.

FIG. 34 is a view illustrating that an access point according to anembodiment of the present invention allocates a channel to a pluralityof stations based on information on an available channel transmitted bya station, and the plurality of stations transmit data to the accesspoint according to the allocated channel.

The second wireless communication terminal may detect an availablechannel and transmit the information on the available channel to thefirst wireless communication terminal. Specifically, a frame transmittedfrom the second wireless communication terminal to the first wirelesscommunication terminal may include information on an available channeldetected by the second wireless communication terminal. At this time, aframe transmitted to the first wireless communication terminal from thesecond wireless communication terminal may be an ACK frame.

The first wireless communication terminal may allocate a channel thatthe second wireless communication terminal is to use for the uplinktransmission to the second wireless communication terminal based onavailable channel information received from the second wirelesscommunication terminal and available channel information detected by thefirst wireless communication terminal. At this time, the first wirelesscommunication terminal may detect an available channel by CCA throughenergy detection. In addition, as described above, the first wirelesscommunication terminal may further receive at least one of informationindicating that there is data to be transmitted by the second wirelesscommunication terminal and the size of data to be transmitted by thesecond wireless communication terminal, and by considering it togetherwith available channel information received from the second wirelesscommunication terminal and available channel information detected by thefirst wireless communication terminal, allocate a channel used foruplink transmission by the second wireless communication terminal to thesecond wireless communication terminal.

In the embodiment of FIG. 34, the access point receives information thatthe third secondary channel Secondary CH #3 is available from the thirdstation. Also, the access point detects that the third secondary channelSecondary CH #3 is available. Therefore, the access point allocates thethird secondary channel Secondary CH #3 as well as the second secondarychannel Secondary CH #2 to the third station, and the third stationtransmits data to the access point through the second secondary channelSecondary CH #2 and the third secondary channel Secondary CH #3. Exceptthis, operations of the access point and the plurality of stations arethe same as those of the embodiment of FIG. 33.

In such an embodiment, without considering whether a channel ispreviously used, the first wireless communication terminal considersonly whether the second wireless communication terminal determines it asa currently available channel and whether it is a first availablechannel, so that the channel usage rate may be increased. However, thereis a high possibility that the data transmission of the second wirelesscommunication terminal causes a collision with the data transmission ofanother wireless communication compared to a case in which a channelthat obtains a TXOP using the RTS frame and the CTS frame is allocated.

As described above, the second wireless communication terminal mayreceive the poll frame from the first wireless communication terminaland terminate the downlink transmission session by transmitting the ACKframe for the poll frame. At this time, the second wirelesscommunication terminal may transmit data to the first wirelesscommunication terminal through a contention procedure. This will bedescribed with reference to FIG. 35.

FIG. 35 is a view illustrating that an access point according to anembodiment of the present invention obtains a TXOP through a contentionprocedure and a CTS-to-Self frame, and a plurality of stations transmitdata to the access point.

The second wireless communication terminal may receive the poll framefrom the first wireless communication terminal and terminate thedownlink transmission session by transmitting the ACK frame for the pollframe. Then, the first wireless communication terminal transmits theCTS-to-Self frame through the contention procedure. Specifically, thefirst wireless communication terminal transmits the CTS-to-Self frame tothe plurality of second wireless communication terminals through achannel allocated to the plurality of second wireless communicationterminals using a contention procedure. In a specific embodiment, thefirst wireless communication terminal may wait for a random value in thecontention window if a channel allocated to the second wirelesscommunication terminal is in an idle state for a predetermined time. Atthis point, the predetermined time may be an AIFS or a DIFS. If thecorresponding channel is in an idle state even after waiting for therandom value, the first wireless communication terminal may transmitdata to the second wireless communication terminal through a channelallocated to the second wireless communication terminal. At this time,the second wireless communication terminal determines whether aCTS-to-Self frame is transmitted through a channel allocated to thesecond wireless communication terminal itself within a predeterminedtime. For convenience of description, the predetermined time is referredto as a UL Timer. When a CTS-to-Self frame is transmitted in the ULTimer, the second wireless communication terminal transmits data to theaccess point through the channel allocated to the second wirelesscommunication terminal itself. If the CTS-to-Self frame is nottransmitted in the UL Timer, the second wireless communication terminaltransmits data to the access point through a channel allocated to thesecond wireless communication terminal itself using the contentionprocedure. Specifically, the second wireless communication terminal maywait for a random value in the contention window when a channelallocated to the second wireless communication terminal is in an idlestate for a predetermined time. At this point, the predetermined timemay be an AIFS or a DIFS. If the channel is in an idle state even afterwaiting for the random value, the second wireless communication terminalmay transmit data to the first wireless communication terminal throughthe channel allocated to the second wireless communication terminalitself.

In such an embodiment, since the first wireless communication terminalperforms the contention procedure based on the UL timer, the UL timer,the contention window, and the TXOP value needs to be appropriately setso that the plurality of second wireless communication terminals mayefficiently transmit data to the first wireless communication terminal.In order to increase the priority of data transmission of the secondwireless communication terminal, the value of the UL timer should belarge, the value of the contention window should be small, and the valueof TXOP should be large. On the contrary, in order to decrease thepriority of data transmission of the second wireless communicationterminal, the value of the UL timer should be small, the value of thecontention window should be large, and the value of TXOP should besmall. The values of the UL timer, the Contention Window (CW), and theTXOP may be defined by the following equations.α>0, β>0, γ>0TXOP=α·TXOP_(base)UL_Timer=β·UL_Timer_(base)CW=γ·CW_(base)

In this case, alpha and beta in the equation are variables in which thevalues increase as the priority of the second wireless communicationterminal data transmission increases, and gamma in the equation is avariable in which the value decreases as the priority of the secondwireless communication terminal data transmission increases. Inaddition, TXOP_(base) is a reference value for TXOP calculation,UL_Timer_(base) is a reference value for calculating a UL timer value,and CW_(base) is a reference value for calculating a CW value.Specifically, at this time, the values of the UL timer, CW, and TXOP maybe changed according to a specific BSS situation.

Also, as described above, the first wireless communication terminalcalculates a random value within a contention window value when achannel allocated to the second wireless communication terminal is in anidle state, and determines whether the corresponding channel is in anidle state after waiting for the calculated random value. If the channelis in an idle state even after waiting for the calculated random value,the first wireless communication terminal transmits a CTS-to-Self framethrough the corresponding channel. At this time, the first wirelesscommunication terminal may obtain a random value a plurality of timesand wait for the minimum value among the obtained random values in orderto give a priority to the data transmission of the second wirelesscommunication terminal. Specifically, the first wireless communicationterminal may obtain a random value as much as the number of the secondwireless communication terminals that are to transmit data to the firstwireless communication terminal, and wait for the minimum value amongthe obtained random values. By this method, probability distributionaccording to the following probability distribution function is shown.

Backoff_(MU − UL) = Min(Backoff_(i))  i  is  index  of  STAs$\begin{matrix}{{{CDFof}\mspace{14mu}{Backoff}} = {{{pr}\left( {{{Min}\left( {Backoff}_{i} \right)} < z} \right)} = {1 -}}} \\{{pr}\left( {{{Min}\left( {Backoff}_{i} \right)} > z} \right)} \\{= {{1 - {\prod\limits_{n}\;{{pr}\left( {{Backoff}_{i} > z} \right)}}} = {1 - \left\lbrack {{pr}\left( {{Backoff}_{i} > z} \right)} \right\rbrack^{n}}}} \\{{= {1 - {\left( \frac{{CW} - z}{CW} \right)^{n}\mspace{14mu}{where}\mspace{14mu} n\mspace{14mu}{is}\mspace{14mu}{number}\mspace{14mu}{of}}}}\mspace{14mu}} \\{{{STAs}\mspace{14mu}{participating}\mspace{14mu}{MU}} - {UL}}\end{matrix}$${{PDF}\mspace{14mu}{of}\mspace{14mu}{Backoff}} = {n\left( \frac{{CW} - z}{CW} \right)}^{n - 1}$

Therefore, if the number n of users increases, the probability that thefirst wireless communication terminal will have a low back-off valueincreases.

In the embodiment of FIG. 35, a plurality of stations that receive apoll frame transmit an ACK frame to the access point.

Thereafter, the access point determines whether a channel allocated tothe plurality of stations during a DIFS time is in an idle state.According to a specific embodiment, the access point can determine if achannel allocated to a plurality of stations during the AIFS time periodis idle. If the channel allocated to the plurality of stations is in anidle state, the access point obtains a random value in a contentionwindow and determines whether the corresponding channel is in an idlestate. At this time, the access point may obtain a random value as muchas the number of stations that are to transmit data to the access pointas described above and wait for the minimum value among the obtainedrandom values. When the corresponding channel is in an idle state, theaccess point transmits a CTS-to-Self frame to a plurality of stationsthrough a channel allocated to the plurality of stations. Specifically,in the embodiment of FIG. 35, the access point transmits the CTS-to-Selfframe to the first station through the primary channel Primary CH. Also,the access point transmits the CTS-to-Self frame to the second stationthrough the first secondary channel Secondary CH #1. Also, the accesspoint transmits the CTS-to-Self frame to the third station through thesecond secondary channel Secondary CH #2 and the third secondary channelSecondary CH #3. Also, the access point transmits the CTS-to-Self frameto the sixth station through the fourth secondary channel Secondary CH#4 and the fifth secondary channel Secondary CH #5. Also, the accesspoint transmits the CTS-to-Self frame to the seventh station through thesixth secondary channel Secondary CH #6 and the seventh secondarychannel Secondary CH #7.

The plurality of stations that receive the CTS-to-Self frame transmitdata to the access point through the allocated channel. Specifically,the first station transmits data to the access point through the primarychannel Primary CH. Also, the second station transmits data to theaccess point through the first secondary channel Secondary CH #1. Also,the third station transmits a data frame to the access point through thesecond secondary channel Secondary CH #2 and the third secondary channelSecondary CH #3. Also, the sixth station transmits a data frame to theaccess point through the fourth secondary channel Secondary CH #4 andthe fifth secondary channel Secondary CH #5. Also, the seventh stationtransmits a data frame to the access point through the sixth secondarychannel Secondary CH #6 and the seventh secondary channel Secondary CH#7.

As described above, the frame transmitted from the second wirelesscommunication terminal to the first wireless communication terminal mayindicate that there is data to be transmitted from the second wirelesscommunication terminal to the first wireless communication terminal. Ina specific embodiment, an ACK frame transmitted from the second wirelesscommunication terminal to the first wireless communication terminal mayindicate that there is data to be transmitted from the second wirelesscommunication terminal to the first wireless communication terminal.Specifically, by setting a specific field of the ACK frame to a specificvalue, it is possible to indicate that there is data to be transmittedfrom the second wireless communication terminal to the first wirelesscommunication terminal.

In addition, the second wireless communication terminal may set thevalue of the duration field in a frame indicating that there is data tobe transmitted based on the time required for data transmission.Accordingly, the NAV of a neighbor wireless communication terminal thatreceives the frame indicating that there is data to be transmitted maybe reset. Accordingly, when the second wireless communication terminaltransmits data through the allocated channel, it is possible to preventanother wireless communication terminal from accessing the correspondingchannel.

At this time, when there is no data to be transmitted from the secondwireless communication terminal to the first wireless communicationterminal, the second wireless communication terminal may transmit theconventional ACK frame in which a specific field is not set to aspecific value. Through this, the second wireless communication terminalhaving no data to be transmitted to the first wireless communicationterminal may quickly return the allocated channel. Specific embodimentswill be described with reference to FIGS. 36 and 37.

FIG. 36 is a view illustrating data transmission between an access pointand a plurality of stations when there is no data to be transmitted tothe access point by some of the plurality of stations according to anembodiment of the present invention.

In the embodiment of FIG. 36, the first station, the second station, thesixth station, and the seventh station have data to be transmitted tothe access point. Accordingly, the first station, the second station,the sixth station, and the seventh station notify the access point thatthere is data to be transmitted through an ACK frame for the datatransmission of the access point. However, since there is no data to betransmitted to the access point, the third station and the fifth stationtransmit the conventional ACK frame and return the correspondingchannel. The other operations of the access point and the plurality ofstations are the same as those of the above-described embodiments.

FIG. 37 is a view illustrating data transmission between an access pointand a plurality of stations when there is no data to be transmitted tothe access point by the plurality of stations according to an embodimentof the present invention.

In the embodiment of FIG. 37, the first station, the second station, thethird station, the fifth station, the sixth station, and the seventhstation receive data from the access point. Since the first station, thesecond station, the third station, the fifth station, the sixth station,and the seventh station do not have any data to be transmitted to theaccess point, the conventional ACK frame is transmitted to return theallocated channel.

In such a manner, when there is no data to be transmitted from thesecond wireless communication terminal to the first wirelesscommunication terminal, operations in an embodiment of the presentinvention are performed identical to those of the legacy wirelesscommunication terminal. Therefore, a transmission method between aplurality of wireless communication terminals according to an embodimentof the present invention does not cause the performance degradation of awireless communication terminal in the legacy environment.

In the above-described embodiment, when the second wirelesscommunication terminal transmits a frame indicating whether there isdata to be transmitted, the first wireless communication terminalimmediately transmits a frame including the information of a channelallocated to the second wireless communication terminal. In such a case,the first wireless communication terminal should receive the frameindicating whether there is data to be transmitted by the secondwireless communication terminal, immediately allocate a channel to thesecond wireless communication terminal, and perform transmissionscheduling. Therefore, in such an embodiment, it may be insufficient forthe first wireless communication terminal to perform the efficientchannel allocation and adjust the transmission schedule for anothersecond wireless communication terminal. Therefore, there is a need foran embodiment to solve this problem. This will be described withreference to FIG. 38. In addition, as described above, the frameincluding the information of the channel allocated to the secondwireless communication terminal may be referred to as a trigger frame ora poll frame.

FIG. 38 is a view illustrating that an access point according to anotherembodiment of the present invention transmits a trigger frame to aplurality of stations.

When a channel is in an idle state for a predetermined time, the firstwireless communication terminal transmits a trigger frame through acontention procedure on the corresponding channel. At this point, thechannel may be the primary channel. In another specific embodiment, thechannel may be a channel allocated to the second wireless communicationterminal for the data transmission of the second wireless communicationterminal. Specifically, when the channel is in idle state for apredetermined time, the first wireless communication terminal calculatesa random value in the contention window. Thereafter, the first wirelesscommunication terminal waits for the calculated random value. If thechannel is in an idle state even after waiting for the calculated randomvalue, the first wireless communication terminal transmits a triggerframe through the corresponding channel. At this time, the trigger framemay indicate that a specific channel is allocated to the second wirelesscommunication terminal, as well as indicate that the second wirelesscommunication terminal randomly accesses a specific range of channels.

The second wireless communication terminal receives the trigger frame.

The second wireless communication terminal obtains information on thechannel allocated to the second wireless communication terminal itselfbased on the trigger frame. At this time, the information on theallocated channel may be the above-described channel vector information.Further, the information on the allocated channel may be informationindicating that the channel is able to randomly access a specific rangeof channels.

The second wireless communication terminal transmits data to the firstwireless communication terminal through the channel allocated to thesecond wireless communication terminal itself. In such a manner, thesecond wireless communication terminal transmits data immediatelywithout transmitting the ACK frame for the trigger frame. At this time,when the first wireless communication terminal receives data from anyone of the plurality of second wireless communication terminals thatallocate channels through the trigger frame, it determines that thetransmission of the trigger frame is successful. Accordingly, when datais received from any one of the second wireless communication terminals,the first wireless communication terminal does not perform a procedurefor a transmission failure such as an increase in the size of thecontention window. When the information on the allocated channelindicated by the trigger frame indicates only random access, the firstwireless communication terminal determines that the transmission issuccessful even if the first wireless communication terminal fails toreceive data. Therefore, even if the first wireless communicationterminal does not receive data, it does not perform a procedure for thetransmission failure.

As described above, the second wireless communication terminal maytransmit to the first wireless communication terminal a frame indicatingwhether there is data to be transmitted to the first wirelesscommunication terminal. This will be described in detail with referenceto FIGS. 39 to 41.

FIG. 39 is a view illustrating a structure of a frame indicating thatthere is data to be transmitted to an access point by a stationaccording to another embodiment of the present invention.

The second wireless communication terminal may indicate whether there isdata to be transmitted to the first wireless communication terminalthrough the specific field value of a frame transmitted to the firstwireless communication terminal. Specifically, the second wirelesscommunication terminal may indicate whether there is data to betransmitted to the first wireless communication terminal through themore data field value of a frame transmitted to the first wirelesscommunication terminal. For example, when there is data to betransmitted to the first wireless communication terminal, the secondwireless communication terminal may set the value of the more data fieldof a frame to be transmitted to the first wireless communicationterminal to 1. The more data field is a field included in the framecontrol field of a MAC frame. Specifically, the more data fieldindicates that there is a bufferable unit (BU) to be transmitted from anaccess point to a station in a power saving (PS) mode. Therefore, astation receiving a frame in which the more data field is 1 continuouslywakes up in the PS mode and waits for the data transmission of an accesspoint. However, if the access point is not in a downlink transmissionsession for transmitting data to the station, the more data field is notused. Accordingly, as described above, the second wireless communicationterminal may use the more data field to notify whether there is data tobe transmitted to the first wireless communication terminal.

At this time, the frame transmitted by the second wireless communicationterminal may be an uplink data frame transmitted from the secondwireless communication terminal to the first wireless communicationterminal. Moreover, the frame transmitted by the second wirelesscommunication terminal may be at least one of an ACK frame and a blockACK frame for data transmitted by the first wireless communicationterminal.

The first wireless communication terminal receiving such a frame mayperform scheduling on the plurality of second wireless terminals andallocate a channel to the plurality of second wireless communicationterminals. Specifically, when the value of the field indicating whetherthere is data to be transmitted to the first wireless communicationterminal in the frame received by the first wireless communicationterminal indicates that there is data to be transmitted to the firstwireless communication terminal, the first wireless communicationterminal adds the second wireless communication terminal that transmitsthe corresponding frame to a scheduling list for channel allocation.Additionally, when the value of the field indicating whether there isdata to be transmitted to the first wireless communication terminal inthe frame received by the first wireless communication terminalindicates that there is no data to be transmitted to the first wirelesscommunication terminal, the first wireless communication terminaldeletes the second wireless communication terminal that transmits thecorresponding frame from the scheduling list for channel allocation.

Further, the first wireless communication terminal transmits a triggerframe including information on an allocated channel to the secondwireless communication terminal.

If the second wireless communication terminal does not receive a triggerframe for a predetermined time after transmitting the frame indicatingthat there is data to be transmitted to the first wireless communicationterminal, it transmits data through a contention procedure as before. Atthis time, the second wireless communication terminal may set a fieldvalue indicating whether there is data to be transmitted to the firstwireless communication terminal in the frame for transmitting the datato “no data to be transmitted”. For example, the second wirelesscommunication terminal may set the value of the more data field in theframe for transmitting data to 0. The predetermined time during whichthe second wireless communication terminal waits may be a timer valueaccording to an access category (AC). The first wireless communicationterminal that receives the frame indicating that there is no data to betransmitted does not include the channel allocation information on thefirst wireless communication terminal that transmits the correspondingframe in the trigger frame.

FIG. 40 is a view illustrating that a plurality of stations according toanother embodiment of the present invention notifies an access pointwhether there is data to be transmitted through an ACK frame.

In the embodiment of FIG. 40, the access point transmits data to thefirst station to the seventh station.

The first station to the seventh station receive the data from theaccess point.

The first station, the second station, the third station, the fifthstation, the sixth station, and the seventh station transmit an ACKframe indicating that there is data to be transmitted to the accesspoint. Specifically, the first station, the second station, the thirdstation, the fifth station, the sixth station, and the seventh stationtransmit an ACK frame in which a value of the more data field is 1 tothe access point. The fourth station transmits an ACK frame indicatingthat there is no data to transmit to the access point. Specifically, thefourth station transmits an ACK frame in which a value of the more datafield is 0 to the access point.

The access point transmits a trigger frame to the first station, thesecond station, the third station, the fifth station, the sixth station,and the seventh station.

The first station, the second station, the third station, the fifthstation, the sixth station, and the seventh station obtain informationon the channel allocated to each of first station, the second station,the third station, the fifth station, the sixth station, and the seventhstation based on the trigger frame.

The first station, the second station, the third station, the fifthstation, the sixth station, and the seventh station transmit data to theaccess point through the channel allocated to each of the first station,the second station, the third station, the fifth station, the sixthstation, and the seventh station.

FIG. 41 is a view illustrating that a plurality of stations according toanother embodiment of the present invention notifies an access pointwhether there is data to be transmitted through an uplink transmissiondata frame.

The first station to the seventh station transmit data to the accesspoint. At this time, the first station, the second station, the thirdstation, the fifth station, the sixth station, and the seventh stationtransmit a data frame indicating that there is data to be transmitted tothe access point to the access point. Specifically, the first station,the second station, the third station, the fifth station, the sixthstation, and the seventh station transmit a data frame in which a valueof the more data field is 1.

The access point transmits an ACK frame to the first station to theseventh station.

The other operations of the access point and the plurality of stationsare the same as those of the above-described embodiment of FIG. 40.

In such a manner, the second wireless communication terminal maytransmit a frame indicating whether there is data to be transmitted tothe first wireless communication terminal, which is in the secondwireless communication terminal's own buffer status. The first wirelesscommunication terminal may efficiently allocate a channel and a scheduleto the plurality of second wireless communication terminals based on thebuffer status of the second wireless communication terminal. Throughthis, the plurality of second wireless communication terminals mayefficiently transmit data to the first wireless communication terminals.

Operations of the first wireless communication terminal and the secondwireless communication terminal according to the above-describedembodiments will be described with reference to FIGS. 42 and 43.

FIG. 42 is a ladder diagram illustrating an operation in which a firstwireless communication terminal transmits data to a second wirelesscommunication terminal according to an embodiment of the presentinvention.

The first wireless communication terminal 400 transmits a trigger frameto the second wireless communication terminal 500 (S301). The triggerframe includes information on a channel allocated to the plurality ofsecond wireless communication terminals 500 in order to communicate withthe first wireless communication terminal 400. At this time, the triggerframe may be referred to as a poll frame as described above. Inaddition, the first wireless communication terminal 400 may transmit atrigger frame to the plurality of second wireless communicationterminals 500 through the primary channel. In another specificembodiment, the first wireless communication terminal 400 may transmit atrigger frame to the plurality of second wireless communicationterminals 500 through a channel allocated to each of the plurality ofsecond wireless communication terminals 500.

The information of the allocated channel included in the trigger framemay include information on a channel and information on a sub-channel.At this time, the channel information is information on a channel havinga bandwidth greater than the minimum unit frequency bandwidth. Thesub-channel information, as a sub-band included in a channel, isinformation on a sub-channel having a bandwidth less than the minimumunit frequency bandwidth. Specifically, the channel information may bean index indicating a channel. In addition, the sub-channel informationmay be an index representing a sub-channel.

In addition, in a specific embodiment, the first wireless communicationterminal 400 may transmit an RTS-to-Self frame, which is an RTS framehaving the address of the first wireless communication terminal 400 asthe reception address, through a plurality of channels. Through this,the first wireless communication terminal 400 obtains the TXOP of thechannel through which the RTS-to-Self frame is transmitted. In aspecific embodiment, the first wireless communication terminal 400 maytransmit a trigger frame after transmitting an RTS-to-Self frame. Inanother specific embodiment, the first wireless communication terminal400 may transmit an RTS-to-Self frame after transmitting a triggerframe.

In another specific embodiment, the first wireless communicationterminal 400 may transmit an RTS frame including channel informationallocated to the second wireless communication terminal 500 instead of atrigger frame.

The second wireless communication terminal 500 may transmit a CTS frameto the first wireless communication terminal 400 in response to theRTS-to-Self frame through the channel allocated to the second wirelesscommunication terminal 500. In a specific embodiment, when the number ofwireless communication terminals that connect to the first wirelesscommunication terminal 400 at one time is limited, the plurality ofsecond wireless communication terminals 500 may sequentially transmitthe CTS frames. At this time, the plurality of second wirelesscommunication terminals 500 may obtain the transmission order of the CTSframes based on the trigger frame.

The second wireless communication terminal 500 obtains information onthe allocated channel based on the frame received from the firstwireless communication terminal 400 (S303).

The first wireless communication terminal 400 transmits data to thesecond wireless communication terminal 500 through the channel allocatedto the second wireless communication terminal 500 (S305). At this time,the first wireless communication terminal 400 may synchronize the dataairtime with the data airtime of the second wireless communicationterminal 500. Specifically, the first wireless communication terminal400 may synchronize the data airtime with the data airtime of anothersecond wireless communication terminal 500 using at least one of paddingand fragmentation. In another specific embodiment, the first wirelesscommunication terminal 400 does not synchronize the data airtime withthe data airtime of another second wireless communication terminal 500,but determines the data airtime according to the amount of data to betransmitted to the second wireless communication terminal 500. In aspecific embodiment, the first wireless communication terminal 400 maytransmit data to the plurality of second wireless communicationterminals 500 through plural terminal A-MPDUs.

FIG. 43 is a ladder diagram illustrating an operation in which a secondwireless communication terminal transmits data to a first wirelesscommunication terminal according to an embodiment of the presentinvention.

The second wireless communication terminal 500 transmits a frameindicating whether there is data to be transmitted to the first wirelesscommunication terminal 400 to the first wireless communication terminal400 (S501). At this time, a specific field of the frame indicatingwhether there is data to be transmitted to the first wirelesscommunication terminal 400 may indicate whether there is data to betransmitted. In a specific embodiment, the more data field of the frameindicating whether there is data to be transmitted to the first wirelesscommunication terminal 400 may indicate whether there is data to betransmitted. For example, when a value of the more data field of theframe indicating whether there is data to be transmitted to the firstwireless communication terminal 400 is 1, this may indicate that thereis data to be transmitted to the first wireless communication terminal400. In addition, the frame indicating whether there is data to betransmitted to the first wireless communication terminal 400 may be atleast one of an ACK frame, a block ACK frame, and an uplink data frametransmitted from the second wireless communication terminal 500 to thefirst wireless communication terminal 400.

Furthermore, the frame indicating whether there is data to betransmitted may include at least any one of the size of data to betransmitted to the first wireless communication terminal 400 andinformation on an available channel detected by the second wirelesscommunication terminal 500.

The first wireless communication terminal 400 transmits a trigger frameto the second wireless communication terminal 500 (S503). The triggerframe includes information on a channel allocated to the plurality ofsecond wireless communication terminals 500 for communication with thefirst wireless communication terminal 400. At this time, the triggerframe may be the same as one described with reference to FIG. 42.Specifically, the first wireless communication terminal 400 may transmita trigger frame based on the frame indicating whether there is data tobe transmitted from the second wireless communication terminal 500. In aspecific embodiment, the first wireless communication terminal 400 mayallocate a channel to the second wireless communication terminal 500based on the frame indicating whether there is data to be transmittedfrom the second wireless communication terminal 500. In addition, thefirst wireless communication terminal 400 may perform scheduling basedon the frame indicating whether there is data to be transmitted from thesecond wireless communication terminal 500. The first wirelesscommunication terminal 400 may generate a trigger frame based on suchchannel allocation and scheduling. In addition, when the channelallocated to the second wireless communication terminal 500 is in anidle state for more than a predetermined time, the first wirelesscommunication terminal 400 may transmit the trigger frame to the secondwireless communication terminal 500 through the corresponding channel.At this point, the predetermined time may be an AIFS or a DIFS. In aspecific embodiment, the first wireless communication terminal 400 mayreceive the ACK frame for the trigger frame from the second wirelesscommunication terminal 500 and may transmit the CTS frame to the secondwireless communication terminal 500.

The second wireless communication terminal 500 obtains information onthe allocated channel based on the frame received from the firstwireless communication terminal 400 (S505).

The second wireless communication terminal 500 transmits data to thefirst wireless communication terminal 400 through the channel allocatedto the second wireless communication terminal 500 (S507). In a specificembodiment, the second wireless communication terminal 500 may transmitdata to the first wireless communication terminal 400 through thechannel allocated to the second wireless communication terminal 500after the first wireless communication terminal 400 transmits theCTS-to-Self frame.

Although the present invention is described by using wireless LANcommunication as an example, it is not limited thereto and may beapplied to other communication systems such as cellular communication.Additionally, while the method, device, and system of the presentinvention are described in relation to specific embodiments thereof,some or all of the components or operations of the present invention maybe implemented using a computer system having a general purpose hardwarearchitecture.

The features, structures, and effects described in the above embodimentsare included in at least one embodiment of the present invention and arenot necessary limited to one embodiment. Furthermore, features,structures, and effects shown in each embodiment may be combined ormodified in other embodiments by those skilled in the art. Therefore, itshould be interpreted that contents relating to such combination andmodification are included in the range of the present invention.

While the present invention is described mainly based on the aboveembodiments but is not limited thereto, it will be understood by thoseskilled in the art that various changes and modifications are madewithout departing from the spirit and scope of the present invention.For example, each component specifically shown in the embodiments may bemodified and implemented. It should be interpreted that differencesrelating to such modifications and application are included in the scopeof the present invention defined in the appended claims.

The invention claimed is:
 1. A base wireless communication terminalcomprising: a transceiver; and a processor, wherein the processor isconfigured to: transmit, by using the transceiver, a first non-dataframe, wherein the first non-data frame reserves a Transmit Opportunity(TXOP), identifies a first plurality of wireless communicationterminals, and allocates a first channel to each of the first pluralityof wireless communication terminals using an index indicatingpredetermined channel usage pattern for a frequency band range, receive,by using the transceiver, at least one second non-data frame through thefirst channel from at least one of the first plurality of wirelesscommunication terminals, simultaneously transmit, by using thetransceiver, a first plurality of data frames to a second plurality ofwireless communication terminals, and simultaneously receive, by usingthe transceiver, a second plurality of data frames from a thirdplurality of wireless communication terminals, through a secondplurality of channels which are allocated to each of the third pluralityof wireless communication terminals, wherein the first plurality of dataframes and the second plurality of data frames are transmitted in theTXOP.
 2. The base wireless communication terminal of claim 1, whereinthe third plurality of wireless communication terminals are notrestricted within the second plurality of wireless communicationterminals.
 3. The base wireless communication terminal of claim 2,wherein the processor is configured to allocate the second plurality ofthe channels within channels, which are used when transmitting from thebase wireless communication terminal to the second plurality of wirelesscommunication terminals is executed before the transmitting of thesecond plurality of data frames, to each of the third plurality ofwireless communication terminals.
 4. The base wireless communicationterminal of claim 1, wherein the processor is configured to synchronizeairtimes of the first plurality of data frames.
 5. The base wirelesscommunication terminal of claim 4, wherein the processor is configuredto pad at least one of the first plurality data frames to synchronizethe air times of the first plurality of data frames.
 6. A wirelesscommunication terminal comprising: a transceiver; and a processor,wherein the processor is configured to receive, by using thetransceiver, a first non-data frame from a base wireless communicationterminal, simultaneously with at least one of a first plurality ofwireless communication terminals, wherein the first non-data framereserves a Transmit Opportunity (TXOP), identifies the first pluralityof wireless communication terminals, and allocates a first channel toeach of the first plurality of wireless communication terminals using anindex indicating predetermined channel usage pattern for a frequencyband range, transmit, by using the transceiver, a second non-data framethrough the first channel to the base wireless communication terminalwhen the first non-data frame indicates an association identifier (ID)of the wireless communication terminal, receive, by using thetransceiver, a first data frame from the base wireless communicationterminal, simultaneously with receiving a second data frame by a secondwireless communication terminal, and transmit, by using the transceiver,a third data frame to the base wireless communication terminal through asecond channel which is allocated to the wireless communicationterminal, simultaneously with transmitting a fourth data frame by athird wireless communication terminal, wherein the first data frame andthe third data frame are transmitted in the TXOP.
 7. The wirelesscommunication terminal of claim 6, wherein the second wirelesscommunication terminal is different from the third wirelesscommunication terminal.
 8. The wireless communication terminal of claim7, wherein the second channel is allocated within channels which areused when transmitting from the base wireless communication terminal tothe wireless communication terminal and the second wirelesscommunication terminal is executed before the transmitting of the thirddata frame.
 9. The wireless communication terminal of claim 6, whereinan airtime of the first data frame is synchronized with an airtime ofthe second data frame.
 10. The wireless communication terminal of claim9, wherein padding is used for the synchronization of the airtime of thefirst data frame with the airtime of the second data frame.
 11. Anoperation method of wireless communication terminal, the methodcomprising: receiving a first non-data frame from a base wirelesscommunication terminal, wherein the non-data frame reserves a TransmitOpportunity (TXOP), identifies the first plurality of wirelesscommunication terminals, and allocates a first channel to each of thefirst plurality of wireless communication terminals using an indexindicating predetermined channel usage pattern for a frequency bandrange, transmitting a second non-data frame through the first channel tothe base wireless communication terminal when the first non-data frameindicates an association identifier (ID) of the wireless communicationterminal, receiving a first data frame from the base wirelesscommunication terminal, simultaneously with receiving a second of dataframe by a second wireless communication terminal, and transmitting athird data frame to the base wireless communication terminal through asecond channel which is allocated to the wireless communicationterminal, simultaneously with transmitting a fourth data frame by athird wireless communication terminal, wherein the first data frame andthe third data frame are transmitted in the TXOP.
 12. The method ofclaim 11, wherein the second wireless communication terminal isdifferent from the fourth wireless communication terminal.
 13. Themethod of claim 12, wherein the second channel is allocated withinchannels which are used when transmitting from the base wirelesscommunication terminal to the wireless communication terminal and thesecond wireless communication terminals is executed before thetransmitting of the third data frame.
 14. The method of claim 11,wherein an airtime of the first data frame is synchronized with anairtime of the second data frame.
 15. The method of claim 14, whereinpadding is used for the synchronization of the airtime of the first dataframe with the airtime of the second data frame.